Traits refactor to support more MCU targets (other than Espressif)

[brainstorm]

This refactor is meant to generalize common functionality and abstract MCU traits so that new targets can be easily ported to SSH Stamp.

Fixes issue #65
Fixes issue #101

... eventually, still yet to decide if this traits architecture works for us.

Read ARCHITECTURE.md for a Birds-eye view about what I'm attempting to put together, let me know if names/structure or whatever looks off!

I.e: probably the MicroPython naming that Julio used is more appropriate: machine/device vs hal/hal-manufacturer.

[Copilot]

Pull request overview

Refactors the project toward a “platform-agnostic core + platform-specific HAL” architecture (issue #65), moving ESP32 hardware details out of the main ssh-stamp crate into dedicated workspace crates and updating OTA tooling accordingly.

Changes:

• Introduces ssh-stamp-hal (traits/config/errors) and ssh-stamp-esp32 (ESP32 implementations + bootable binary).
• Reworks the core ssh-stamp crate to be platform-agnostic (new app entrypoints, PlatformServices abstraction, generic flash store I/O).
• Renames the OTA CLI utility from ota-packer to packer and updates workflows/scripts/docs.

Reviewed changes

Copilot reviewed 59 out of 61 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
storage/src/lib.rs	Removes prior ESP-specific storage + flash singleton from the old storage crate.
storage/src/esp_ota.rs	Removes prior ESP OTA writer implementation from storage.
storage/Cargo.toml	Removes the storage crate manifest (crate no longer part of the workspace).
ssh-stamp-hal/Cargo.toml	Adds new HAL trait crate manifest.
ssh-stamp-hal/src/lib.rs	Defines and re-exports HAL surface (traits/config/errors).
ssh-stamp-hal/src/config.rs	Adds shared UART/WiFi config types for HAL consumers.
ssh-stamp-hal/src/error.rs	Adds unified HalError + peripheral-specific error enums.
ssh-stamp-hal/src/traits/mod.rs	Central trait module/re-exports for peripherals.
ssh-stamp-hal/src/traits/flash.rs	Defines OtaActions trait for OTA partition actions.
ssh-stamp-hal/src/traits/hash.rs	Defines HashHal trait for hash/HMAC operations.
ssh-stamp-hal/src/traits/rng.rs	Defines RngHal trait for RNG operations.
ssh-stamp-hal/src/traits/timer.rs	Defines TimerHal trait for timing/delays.
ssh-stamp-hal/src/traits/uart.rs	Defines UartHal trait for UART read/write/configure.
ssh-stamp-hal/src/traits/network/mod.rs	Adds network trait hierarchy module.
ssh-stamp-hal/src/traits/network/provider.rs	Defines NetworkProviderHal base trait.
ssh-stamp-hal/src/traits/network/wifi.rs	Defines WifiHal extension trait.
ssh-stamp-esp32/Cargo.toml	Adds ESP32 platform crate manifest + per-chip features.
ssh-stamp-esp32/build.rs	Moves ESP32 link-arg setup into the ESP32 crate.
ssh-stamp-esp32/src/lib.rs	ESP32 crate root: re-exports implementations and helpers.
ssh-stamp-esp32/src/flash.rs	Implements flash singleton + EspOtaWriter using ssh-stamp-hal::OtaActions.
ssh-stamp-esp32/src/hash.rs	Provides ESP32 hash/HMAC implementation (currently software-backed).
ssh-stamp-esp32/src/network/mod.rs	Exposes ESP32 network helpers.
ssh-stamp-esp32/src/network/wifi.rs	Implements WifiHal + NetworkProviderHal for ESP32 WiFi AP + DHCP.
ssh-stamp-esp32/src/platform.rs	Implements core PlatformServices for ESP32 (save/reset/OTA/UART-activate).
ssh-stamp-esp32/src/rng.rs	Implements RNG and registers custom getrandom hook on ESP32.
ssh-stamp-esp32/src/timer.rs	Implements TimerHal for ESP32 via embassy_time.
ssh-stamp-esp32/src/uart.rs	Provides buffered UART implementation for the SSH bridge.
ssh-stamp-esp32/src/bin/ssh-stamp-esp32.rs	New ESP32-family binary wiring peripherals then calling platform-agnostic app.
src/lib.rs	Makes core crate platform-agnostic; enables strict unused-import/var denies; adds new modules.
src/app.rs	Adds platform-agnostic app entrypoints (prepare_ap_config, run_app).
src/platform.rs	Introduces PlatformServices trait for persistence/reset/OTA/UART activation.
src/store.rs	Generalizes flash store read/write over NorFlash/ReadStorage; adds config migration.
src/settings.rs	Adjusts DEFAULT_IP type and removes per-chip UART pin cfg from core crate.
src/serve.rs	Refactors SSH event loop to delegate to handle module and platform services.
src/serial.rs	Generalizes serial bridge over a BufferedSerial trait (platform-provided).
src/handle.rs	Splits SSH event handling into smaller functions; integrates platform services + OTA writer.
src/config.rs	Makes config creation take platform-provided MAC; exposes SSID/PSK generators for migration.
src/errors.rs	Updates file header (license/copyright).
src/main.rs	Removes old ESP32-specific main from core crate.
src/espressif/mod.rs	Removes old ESP-specific module from core crate.
src/espressif/net.rs	Removes old ESP-specific networking implementation from core crate.
src/espressif/rng.rs	Removes old ESP-specific RNG implementation from core crate.
src/espressif/buffered_uart.rs	Removes old ESP-specific buffered UART implementation from core crate.
src/espressif/hash.rs	Removes old ESP-specific hash placeholder code from core crate.
ota/Cargo.toml	Adds dependency on ssh-stamp-hal; renames bin to packer.
ota/src/lib.rs	Drops otatraits module and re-exports updated packer naming.
ota/src/otatraits.rs	Removes OTA trait definition (now sourced from ssh-stamp-hal).
ota/src/handler.rs	Switches OTA handler to ssh_stamp_hal::OtaActions.
ota/src/sftpserver.rs	Updates SFTP server to new handle init trait; updates status code usage.
ota/src/tlv.rs	Updates TLV parsing context import; rejects unknown TLVs instead of skipping.
ota/src/bin/packer.rs	Renames CLI from ota-packer to packer.
ota/src/bin/README.md	Updates docs to packer naming.
ota/README.md	Updates docs to packer naming.
ota/test-hil-esp32c6-e2e.sh	Updates HIL script to use cargo packer.
docs/ARCHITECTURE.md	Adds architecture documentation explaining the new crate split and invariants.
build.rs	Removes root build script (moved to ESP32 crate).
Cargo.toml	Converts repo into a multi-crate workspace; adds shared workspace deps; updates aliases/features/docs.
Cargo.lock	Updates lockfile for new crates/deps and renamed bin.
.cargo/config.toml	Updates cargo aliases for new package/bin layout and renamed packer.
.github/workflows/tests.yml	Renames OTA job to packer (utility tests).
.github/workflows/build.yml	Updates clippy/build steps to target ssh-stamp-esp32 binary and new packer alias.

[brainstorm]

Sorry folks for the huge changeset, but there's no good way to piecemeal this (I think)... @jubeormk1, if and when you have some time, could you do some of your comprehensive testing again against this PR? Let's make sure I didn't introduce some regression with some bad merge somewhere :-/

Thanks in advance!

PS: I accidentally clicked on Copilot PR review, wasn't meaning that, grr... although some of the suggestions are not bad, actually 🤔