fix(vm/opcode/push,environment,templates,generator,await,new): convert panics to EngineError::Panic using js_expect

[KaustubhOG]

Part of #3241.

Converts all convertible .expect() panics to .js_expect()? in:

• opcode/push/array.rs (4)
• opcode/push/environment.rs (2)
• opcode/push/class/mod.rs (1)
• opcode/push/class/field.rs (8)
• opcode/push/class/private.rs (12)
• opcode/environment/mod.rs (12)
• opcode/templates/mod.rs (7)
• opcode/generator/mod.rs (6)
• opcode/generator/yield_stm.rs (2)
• opcode/await/mod.rs (5)
• opcode/new/mod.rs (2)

Total: 61 panics converted.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,545	50,545	0
Ignored	1,426	1,426	0
Failed	992	992	0
Panics	2	2	0
Conformance	95.43%	95.43%	0.00%

Tested main commit: 0592ecc32629c18d43dc136b6675ef980f37a061
Tested PR commit: 0042a0b56e9bcaed3e28541eeec4be05ca007ae3
Compare commits: 0592ecc...0042a0b

[KaustubhOG]

To this pr i tried one new thing
For functions returning ControlFlow<CompletionRecord>, ? is not available, so js_expect cannot be used directly. A new pattern was introduced using let..else + handle_error + PanicError:

let Some(value) = some_option else {
    return context.handle_error(PanicError::new("msg").into());
};

This ensures panics are still converted to EngineError::Panic without requiring a JsResult context. Happy to revert these if a different approach is preferred.

[codecov]

Codecov Report

❌ Patch coverage is 46.80851% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.85%. Comparing base (6ddc2b4) to head (0042a0b).
⚠️ Report is 916 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/vm/opcode/push/class/private.rs	0.00%	9 Missing ⚠️
core/engine/src/vm/opcode/await/mod.rs	40.00%	6 Missing ⚠️
core/engine/src/vm/opcode/generator/yield_stm.rs	28.57%	5 Missing ⚠️
core/engine/src/vm/opcode/generator/mod.rs	50.00%	4 Missing ⚠️
core/engine/src/vm/opcode/push/array.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5232       +/-   ##
===========================================
+ Coverage   47.24%   59.85%   +12.60%     
===========================================
  Files         476      582      +106     
  Lines       46892    63478    +16586     
===========================================
+ Hits        22154    37992    +15838     
- Misses      24738    25486      +748     

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