feat(fetch): implement bodyUsed and clone() for Request and Response (#4992)

[RajdeepKushwaha5]

Description

Summary

This pull request implements the .clone() method and the .bodyUsed property for both the Request and Response Web APIs in boa_runtime, addressing issue #4992. Previously, cloning a request or response would fail because it wasn't implemented, and body consuming methods weren't properly ensuring that a given buffer is only drained once per spec.

Changes Made

• Added a body_used: Cell<bool> internal state wrapped in #[unsafe_ignore_trace] inside both JsRequest and JsResponse.
• Configured a #[boa(getter)] for bodyUsed returning a boolean for Request and Response.
• Implemented clone() via standard standard JS method binding (clone_js internally mapped to clone), appropriately deep cloning fields (like Headers) while sharing the internal Request/Response structure safely.
• Added a pub fn deep_clone(&self) -> Self standard to JsHeaders inside headers.rs in order to ensure the newly cloned Request/Response has its own distinct map of headers.
• Updated bytes(), text(), and json() within JsResponse to fail eagerly with a TypeError if bodyUsed is currently true. Otherwise, it trips the internal flag and resolves the promise properly.

Testing

• Locally passed cargo clippy -p boa_runtime --all-features with zero warnings.
• Extensively ran cargo test -p boa_runtime resolving all internal checks.
• Adheres to the established specification guidelines and integrates with standard JS error generation patterns using JsNativeError.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,935	49,935	0
Ignored	2,207	2,207	0
Failed	821	821	0
Panics	0	0	0
Conformance	94.28%	94.28%	0.00%

Tested main commit: f5ae9f7385337d34f68fa9969054efe8c0161305
Tested PR commit: 8c01e4484d7abc884589f5b7be103f4ff53764fb
Compare commits: f5ae9f7...8c01e44

[codecov]

Codecov Report

❌ Patch coverage is 38.88889% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.10%. Comparing base (6ddc2b4) to head (8c01e44).
⚠️ Report is 845 commits behind head on main.

Files with missing lines	Patch %	Lines
core/runtime/src/fetch/response.rs	37.83%	23 Missing ⚠️
core/runtime/src/fetch/request.rs	46.66%	8 Missing ⚠️
core/runtime/src/fetch/headers.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5041       +/-   ##
===========================================
+ Coverage   47.24%   59.10%   +11.86%     
===========================================
  Files         476      563       +87     
  Lines       46892    62580    +15688     
===========================================
+ Hits        22154    36988    +14834     
- Misses      24738    25592      +854     

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