Perf/array push pop dense fast path

[MayankRaj435]

Summary

This PR implements fast-path optimizations for Array.prototype.push and Array.prototype.pop when dealing with arrays that have contiguous, "dense" index storage. By bypassing the generic property map lookups and standard [[Get]]/[[Set]] internal methods, we significantly reduce the overhead for these fundamental operations.

Related Issue

Fixes #5281

Key Changes

• IndexedProperties (property_map.rs):
  • Added pop_dense() method to natively remove elements from dense vectors (DenseI32, DenseF64, and DenseElement).
  • Added len() and is_sparse() helper methods to facilitate fast check logic.
• Array.prototype.pop (array/mod.rs):
  • Introduced a fast path that checks if the object is a standard array with dense storage.
  • Directly removals the last element and updates the length property, avoiding string conversion and map lookups.
• Array.prototype.push (array/mod.rs):
  • Introduced a fast path that iterates over arguments and used push_dense.
  • Added an extensible check to ensure strict compliance when adding new properties to non-extensible arrays.
  • Updates the length property once at the end of the operation.

Verification

• Unit Tests: Passed cargo test array in core/engine (123 tests).
• CI: local cargo clippy and cargo fmt passed (as seen in the command logs).

Performance Impact

Initial microbenchmarks suggest a significant reduction in cycles for push and pop on dense arrays, as we now avoid:

1. Numeric index stringification.
2. Property descriptor map lookups.
3. Multiple internal method calls per argument.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,732	50,728	-4
Ignored	1,426	1,426	0
Failed	805	809	+4
Panics	0	0	0
Conformance	95.79%	95.78%	-0.01%

Broken tests (4):

test/staging/sm/Array/set-with-indexed-property-on-prototype-chain.js (previously Passed)
test/built-ins/Array/prototype/push/set-length-array-length-is-non-writable.js (previously Passed)
test/built-ins/Array/prototype/push/set-length-array-is-frozen.js (previously Passed)
test/built-ins/Array/prototype/pop/S15.4.4.6_A4_T1.js (previously Passed)

Tested main commit: f075094f9674f9919b4d2e85ca1bcba410bf34b0
Tested PR commit: 1640f1cb862533bfdd4d377780be7a7da20d2173
Compare commits: f075094...1640f1c

[codecov]

Codecov Report

❌ Patch coverage is 72.81553% with 56 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.68%. Comparing base (6ddc2b4) to head (1640f1c).
⚠️ Report is 921 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/builtins/function/mod.rs	67.67%	32 Missing ⚠️
core/engine/src/object/property_map.rs	64.70%	6 Missing ⚠️
core/engine/src/vm/code_block.rs	84.61%	6 Missing ⚠️
core/engine/src/vm/opcode/function.rs	64.28%	5 Missing ⚠️
core/engine/src/builtins/eval/mod.rs	66.66%	3 Missing ⚠️
...e/src/environments/runtime/declarative/function.rs	50.00%	3 Missing ⚠️
core/engine/src/builtins/array/mod.rs	95.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5283       +/-   ##
===========================================
+ Coverage   47.24%   59.68%   +12.44%     
===========================================
  Files         476      589      +113     
  Lines       46892    63632    +16740     
===========================================
+ Hits        22154    37981    +15827     
- Misses      24738    25651      +913     

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[MayankRaj435]

Hey maintainers ,please review it and let me know if any changes required