[rust-server] Fix panic on binary request bodies coerced to UTF-8

[twistali]

Fixes #24094

Problem

For an endpoint with a format: binary (or format: byte) request body,
the generated rust-server client coerced the body bytes through
String::from_utf8(param_body.0).expect("Body was not valid UTF8") before
placing them in the HTTP request. This panics at runtime on any payload
containing a byte > 127 — i.e. any real binary content (gzip, protobuf,
images, encrypted blobs).

The parameter type is swagger::ByteArray (wrapping Vec<u8>), which
correctly models arbitrary octets — only the request serialization path
assumed text encoding. The response path already handled binary correctly,
and the older rust-server-deprecated (swagger 5/6) templates already emit
Body::from(body), so the defect was isolated to the current rust-server
client request template.

Fix

• client-request-body-instance.mustache: for isBinary/isByteArray
  bodies, pass the raw Vec<u8> through with body_from_bytes(param.0)
  instead of String::from_utf8(...).expect(...).
• client-mod.mustache: add a body_from_bytes(b: Vec<u8>) helper
  mirroring the existing body_from_string.

Tests

• Added a /required_binary_stream (format: binary) endpoint to the
  openapi-v3 rust-server test spec.
• Added RustServerCodegenTest.testBinaryRequestBodyNotCoercedToUtf8,
  asserting the generated client uses body_from_bytes and no longer
  contains the UTF-8 coercion. (Fails against old templates, passes with
  the fix.)
• Regenerated sample compiles cleanly with cargo build.

PR checklist

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---

Summary by cubic

Fixes a runtime panic in rust-server clients by sending raw bytes for binary request bodies instead of coercing to UTF-8. Real binary payloads (gzip, protobuf, images, etc.) now work without crashing.

• Bug Fixes

  • For isBinary/isByteArray request bodies, use body_from_bytes(param.0) in client-request-body-instance.mustache instead of String::from_utf8(...).
  • Add body_from_bytes(b: Vec<u8>) helper in client-mod.mustache, mirroring body_from_string.
  • Explicitly set request bodies for text and XML via body_from_string(...) for consistency.
  • Regenerate samples across rust-server (and rust-server-deprecated) to reflect the fix.

• Tests

  • Add /required_binary_stream endpoint (format: binary) to the Rust server test spec.
  • Add RustServerCodegenTest.testBinaryRequestBodyNotCoercedToUtf8 to assert body_from_bytes is used and UTF-8 coercion is gone.
  • Regenerated samples compile with cargo build.

^{Written for commit 7034d01. Summary will update on new commits.}

[twistali]

Tagging rust-server technical committee for review: @frol @farcaller @richardwhiuk @paladinzh @jacob-pro @dsteele

[cubic-dev-ai]

No issues found across 28 files

_{Re-trigger cubic}

[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/28086139450/job/83154058834?pr=24116 can be ignored.

update: tests for rust-server-deprecated removed via #24117

[wing328]

thanks for the PR which has been merged