perf: skip double deserialization and enable release LTO

[KENILSHAHH]

Summary

• Skip intermediate serde_json::Value parsing for HTTP responses when tracing is disabled, cutting deserialization work in half for normal production usage
• Replace deep Value::clone() with flat Value::to_string() in the tracing deserialization path, reducing many small heap allocations to a single one
• Add [profile.release] with lto = "thin" and codegen-units = 1 to match existing bench profile, enabling cross-crate inlining and more aggressive compiler
  optimizations for release builds

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Note

Medium Risk
Changes the HTTP response deserialization path and cfg gating around serde_helpers, which could surface subtle differences in how optional/unknown fields are handled across feature sets. Build/profile changes (release LTO + single codegen unit) may also affect compile times and binary characteristics but not runtime behavior correctness.

Overview
Improves runtime and build-time performance for the SDK client.

When tracing is disabled, the main HTTP request path now deserializes responses directly into the target type instead of first parsing into serde_json::Value (avoiding a second deserialization pass). When tracing is enabled, the warning/error logging path in deserialize_with_warnings is updated to avoid deep Value cloning by storing a single raw_json string and re-parsing only when needed.

Adds a release profile in Cargo.toml to match bench (lto = "thin", codegen-units = 1) for more aggressive release optimizations.

^{Written by Cursor Bugbot for commit 4b9d385. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.54%. Comparing base (a5dc726) to head (4b9d385).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #315   +/-   ##
=======================================
  Coverage   85.54%   85.54%           
=======================================
  Files          32       32           
  Lines        5167     5168    +1     
=======================================
+ Hits         4420     4421    +1     
  Misses        747      747           

Flag	Coverage Δ
rust	85.54% <100.00%> (+<0.01%)	⬆️

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