Stellar-xdr compilation fails due to missing `try_size_hint` methods in Arbitrary derive

[samjay8]

Title: fix: stellar-xdr compilation fails due to missing try_size_hint methods in Arbitrary derive

Labels: bug, backend, rust, dependencies, priority-high

Description:
The project fails to compile because the stellar-xdr
dependency generates hundreds of Rust compilation errors
related to missing try_size_hint methods while deriving
Arbitrary.

The errors originate from generated files inside the
stellar-xdr crate and appear to be caused by a dependency
or feature mismatch between stellar-xdr, arbitrary,
and the current Rust/Soroban ecosystem versions.

This completely blocks compilation of the contracts
workspace and prevents development, testing, and deployment.

Error:
error[E0599]: no function or associated item named
try_size_hint found for struct RestoreFootprintOp
in the current scope

Additional repeated errors:

• OperationBody
• Operation
• HashIdPreimage
• Memo
• Transaction
• TransactionEnvelope
• SorobanTransactionData
• InvokeHostFunctionResult
• OperationResult
• TransactionResult
• Many other generated XDR types

Final compiler output:
error: could not compile stellar-xdr (lib)
due to 1836 previous errors

This is a critical issue because the entire smart contract
workspace cannot compile successfully.

Likely Cause:
The issue is most likely caused by one of the following:

• Version incompatibility between:

  • stellar-xdr
  • soroban-sdk
  • arbitrary
  • Rust toolchain version

• An incompatible arbitrary crate version that does not
  expose the expected try_size_hint API

• Incorrect crate features being enabled for stellar-xdr

• A transitive dependency conflict introduced during
  dependency updates

What Needs to Be Done:

Option A — Align Soroban/Stellar dependency versions (preferred):

• Verify compatible versions for:
  • soroban-sdk
  • stellar-xdr
  • soroban-env-*
  • stellar-strkey
• Use officially compatible versions from the Soroban SDK
  release documentation
• Update Cargo.toml dependencies accordingly
• Run:
  cargo update
• Rebuild the workspace

Option B — Pin the arbitrary crate version:

• Inspect dependency tree:
  cargo tree | grep arbitrary
• Identify incompatible versions
• Pin a compatible arbitrary version in Cargo.toml
• Rebuild dependencies

Option C — Disable problematic crate features:

• Inspect whether the arbitrary feature is enabled
  unnecessarily on stellar-xdr
• Remove or disable:
  features = ["arbitrary"]
  if fuzzing/property testing is not required
• Rebuild the workspace

Option D — Update Rust toolchain:

• Verify the Rust version matches the Soroban-supported
  toolchain version
• Run:
  rustup update
  rustup override set stable
• Rebuild after toolchain alignment

Key Files:

• Cargo.toml
• Cargo.lock
• apps/contracts/Cargo.toml
• Any workspace dependency configuration files
• .cargo/config.toml (if present)

Commands to Investigate:

• cargo tree | grep arbitrary
• cargo tree | grep stellar-xdr
• cargo tree | grep soroban
• rustc --version
• cargo clean
• cargo build

Acceptance Criteria:

• cargo build completes successfully
• stellar-xdr compiles without try_size_hint errors
• No Arbitrary derive failures remain
• Soroban contracts compile successfully
• Dependency versions are aligned and documented
• Existing tests continue to pass
• No duplicate or conflicting dependency versions exist
  in the workspace

Branch: fix/stellar-xdr-arbitrary-compile-failure

Commit: fix(deps): resolve stellar-xdr Arbitrary derive compilation failure