feat(engine): introduce 'arena lifetime plumbing and eager AST compilation

[akash-R-A-J]

This Pull Request fixes/closes #4929 .

It introduces 'arena lifetime plumbing across the AST, parser, and engine and adjusts the compilation architecture to ensure arena-bound AST lifetimes do not escape into runtime structures.

It changes the following:

• Eager Compilation Architecture: Refactored the engine to compile AST nodes to bytecode immediately after parsing. This allows the AST (and its 'arena lifetime) to be dropped before execution begins.

• Lifetime Isolation: Prevents the 'arena lifetime from leaking into long-lived runtime structures such as Script and Module, keeping them compatible with Boa's GC-managed runtime.

• AST Architecture: Introduced the 'arena lifetime parameter to core AST nodes and structures in boa_ast.

• Parser Integration: Propagated the 'arena lifetime through boa_parser, allowing the parser to return arena-bound AST structures that are immediately consumed by the compiler.

• Engine Support: Updated ByteCompiler, optimizer infrastructure, and module compilation paths to propagate the 'arena lifetime through the compilation pipeline.

Verification:

• cargo check --workspace passes
• cargo test --workspace passes
• cargo clippy --workspace --all-targets --all-features -- -D warnings clean

This PR establishes the foundation for arena-allocated AST nodes by ensuring 'arena references remain confined to the parsing and compilation stages and do not escape into runtime state.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,687	49,687	0
Ignored	2,262	2,262	0
Failed	1,014	1,014	0
Panics	0	0	0
Conformance	93.81%	93.81%	0.00%

Tested main commit: b3d820369072123ded8defc927405b99b9012648
Tested PR commit: fa5608cce76facc090eac1e1b2caec248f7325f1
Compare commits: b3d8203...fa5608c

[codecov]

Codecov Report

❌ Patch coverage is 84.20221% with 100 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.60%. Comparing base (6ddc2b4) to head (fa5608c).
⚠️ Report is 775 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/module/source.rs	61.53%	35 Missing ⚠️
core/ast/src/operations/mod.rs	83.54%	13 Missing ⚠️
core/engine/src/bytecompiler/mod.rs	75.75%	8 Missing ⚠️
core/ast/src/module_item_list/mod.rs	37.50%	5 Missing ⚠️
core/ast/src/visitor.rs	75.00%	4 Missing ⚠️
.../parser/src/parser/statement/declaration/import.rs	75.00%	4 Missing ⚠️
core/ast/src/expression/operator/binary/mod.rs	66.66%	3 Missing ⚠️
core/ast/src/expression/new.rs	60.00%	2 Missing ⚠️
core/ast/src/function/async_generator.rs	66.66%	2 Missing ⚠️
core/ast/src/function/generator.rs	66.66%	2 Missing ⚠️
... and 20 more

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4930       +/-   ##
===========================================
+ Coverage   47.24%   57.60%   +10.36%     
===========================================
  Files         476      556       +80     
  Lines       46892    61074    +14182     
===========================================
+ Hits        22154    35184    +13030     
- Misses      24738    25890     +1152     

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[akash-R-A-J]

Hey @jedel1043, could you review this PR when you get a chance? Happy to address any questions or requested changes.

Here are the benchmark results: