fix(volo-build): gate multiservice binary codec behind unsafe-codec

[shenyj3]

Summary

• The raw-bytes service impl generated by volo-build for Router-based multi-service servers unconditionally decoded requests with TBinaryUnsafeInputProtocol, whose read primitives use get_unchecked without bounds checks.
• A truncated/malformed thrift binary frame from any unauthenticated peer could trigger an out-of-bounds heap read (debug: abort; release: silent OOB), bypassing the unsafe-codec feature that guards the single-service codec in codec/default/thrift.rs.
• Move encode/decode into new volo_thrift::codec::default::multiservice helpers that use the safe TBinaryProtocol by default and the unsafe variants only behind unsafe-codec; the compact path is unchanged.

Test plan

• cargo check -p volo-thrift with default features and --features unsafe-codec
• cargo check --workspace --offline
• New regression test thrift_multi_service_malformed: truncated framed binary frame against a Router server; the default safe codec survives (debug + release) and a subsequent normal request succeeds
• Same binary built with --features volo-thrift/unsafe-codec aborts at pilota binary_unsafe.rs precondition, confirming the test hits the fix point
• Existing thrift_multi_service tests pass; fmt + clippy clean

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.59%. Comparing base (90aa52b) to head (cdbd4bc).

Files with missing lines	Patch %	Lines
volo-thrift/src/codec/default/multiservice.rs	83.33%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #671      +/-   ##
==========================================
+ Coverage   56.14%   61.59%   +5.45%     
==========================================
  Files         166      167       +1     
  Lines       22517    22606      +89     
==========================================
+ Hits        12642    13924    +1282     
+ Misses       9875     8682    -1193     

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