fix(rust-client): Drain discarded response bodies

[lcian]

The Rust client now consumes response bodies on error and on successful paths that otherwise discard them, allowing the underlying HTTP connections to return cleanly to the connection pool.
Successful GET responses remain caller-owned streams, while JSON responses continue to be consumed by deserialization.

Special case: batch multipart responses remain non-drained, as that would require buffering the whole batch response at once due to a limitation in multer.

[codecov]

Codecov Report

❌ Patch coverage is 68.83117% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.10%. Comparing base (a48ebfc) to head (e302999).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
clients/rust/src/resumable.rs	0.00%	21 Missing ⚠️
clients/rust/src/get.rs	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #629      +/-   ##
==========================================
+ Coverage   89.08%   89.10%   +0.01%     
==========================================
  Files         112      114       +2     
  Lines       20560    20748     +188     
==========================================
+ Hits        18316    18487     +171     
- Misses       2244     2261      +17     

Components	Coverage Δ
Rust Backend	93.53% <ø> (+0.04%)	⬆️
Rust Client	72.66% <68.83%> (-0.05%)	⬇️
Python Client	93.56% <ø> (ø)

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[jan-auer]

What a name :)
Thanks!