fix: support type aliases in binding files (#172)

[lirenjie95]

Summary

Using a type alias (e.g. pub type Amount = i64;) as a parameter or struct field type in an r2g binding file used to crash codegen (Option::unwrap() on a None in rust2go-common) or emit references to a nonexistent AmountRef. This PR makes type aliases work in binding files.

Fixes #172

Changes

• rust2go-common/src/common.rs:
  • RawRsFile::new now expands non-generic type aliases at parse time: alias chains are resolved (type A = B; type B = i64;), cycles are reported with a clear panic message, and usages are expanded recursively inside generic arguments (e.g. Vec<Alias>). Expansion applies to struct field types and trait method params/return types.
  • Added ParamType::to_rust_ref_assoc, rendering the ref type as <T as ::rust2go::ToRef>::Ref — this form is correct for both concrete types and aliases (the alias shares the underlying type's ToRef impl).
  • Unit tests for the expansion (primitives, chains, Vec<Alias>, struct fields, trait params/returns).
• rust2go-common/src/r2g.rs: use to_rust_ref_assoc for response ref types in generated callbacks (3 sites) — the proc-macro side cannot resolve aliases itself.
• rust2go-macro/src/lib.rs: r2g_derive emits <#ty as ::rust2go::ToRef>::Ref for non-primitive ref fields instead of assuming a {ty}Ref type name.
• test/: end-to-end coverage — pub type UserId = u64; used in a struct field (BalanceRequest), a sync trait method, and an async #[drop_safe] method with bare-alias params/return; Go impl + regenerated bindings + Rust tests.

Testing

• Reproduced the panic with a minimal case before the fix; after the fix the generated gen.go expands alias fields to uint64_t and Go signatures use *uint64.
• cargo fmt --check, cargo clippy --workspace --all-features --all-targets -- --deny warnings, and the full test suite (workspace, with mem-ring tested separately due to the known unrelated workspace feature-unification issue) all pass locally.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.00000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.52%. Comparing base (1779a40) to head (d2a9b99).

Files with missing lines	Patch %	Lines
rust2go-common/src/common.rs	95.48%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #174      +/-   ##
==========================================
+ Coverage   82.84%   83.52%   +0.68%     
==========================================
  Files          18       18              
  Lines        3503     3672     +169     
==========================================
+ Hits         2902     3067     +165     
- Misses        601      605       +4     

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