fix(storage): reject invalid device and engine configs

[mjc]

Move default-capacity discovery and storage-engine validation out of panic paths and into fallible, type-driven APIs.

What changed:

• FileDeviceBuilder now probes block-device capacity or parent-directory free space through fallible helpers instead of unwrap/expect.
• FsDeviceBuilder now computes default capacity lazily and returns Error if filesystem probing fails.
• BlockEngineConfig and UringIoEngineConfig now use NonZeroUsize for counts and depths, so zero values are rejected at compile time for normal callers.
• CPU pinning now uses nonempty CPU sets to set thread count, leaves pinning off when the CPU set is empty, and rejects mismatched with_cpus(...) / with_threads(...) combinations up front.

Tests added:

• test_file_device_builder_rejects_path_without_parent
• test_fs_device_builder_propagates_dir_creation_errors
• test_uring_empty_cpu_sets_disable_pinning
• test_uring_rejects_mismatched_cpu_count

[mjc]

Tightened the io_uring CPU affinity path a bit more: a nonempty CPU list still sets the thread count, but we now reject mismatched with_cpus(...) / with_threads(...) combinations up front instead of letting them reach an index panic in build(). Added tests for both the mismatch and the empty-list “disable pinning” case.

[codecov]

Codecov Report

❌ Patch coverage is 87.58621% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
foyer-storage/src/io/engine/uring.rs	88.40%	8 Missing ⚠️
foyer-storage/src/io/device/file.rs	77.27%	5 Missing ⚠️
foyer-bench/src/main.rs	50.00%	1 Missing ⚠️
foyer-storage/src/engine/block/engine.rs	96.66%	1 Missing ⚠️
foyer-storage/src/io/device/fs.rs	88.88%	1 Missing ⚠️
foyer-storage/src/io/engine/mod.rs	85.71%	1 Missing ⚠️
foyer-storage/src/store.rs	83.33%	1 Missing ⚠️

Files with missing lines	Coverage Δ
foyer-bench/src/main.rs	70.02% <50.00%> (+0.22%)	⬆️
foyer-storage/src/engine/block/engine.rs	93.46% <96.66%> (-0.08%)	⬇️
foyer-storage/src/io/device/fs.rs	92.30% <88.88%> (+0.47%)	⬆️
foyer-storage/src/io/engine/mod.rs	94.66% <85.71%> (-1.05%)	⬇️
foyer-storage/src/store.rs	86.33% <83.33%> (-0.10%)	⬇️
foyer-storage/src/io/device/file.rs	70.17% <77.27%> (+7.31%)	⬆️
foyer-storage/src/io/engine/uring.rs	87.81% <88.40%> (+0.85%)	⬆️

... and 2 files with indirect coverage changes

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[mjc]

I'll be back at this in a couple days to add more tests if y'all need, I try not to leave drive-by PRs. just ran out of time.

--

我过几天会再回来继续补测试，如果你们需要的话。我尽量不留那种丢完就跑的 PR，只是这次实在没时间了。