Fix delete with optional chaining not actually deleting properties

[Ansh-699]

Description

delete with optional chaining (?.) returned true but did not actually delete the property.

Root Cause

Access::from_expression() has no arm for Expression::Optional, so the delete compilation falls to the else branch that just evaluates the expression and pushes true without emitting a delete opcode.

Fix

Added compile_optional_delete and compile_optional_delete_final methods in the bytecompiler (mod.rs). These walk the optional chain, compile intermediate accesses normally, and emit DeletePropertyByName/DeletePropertyByValue for the final chain item. A new Expression::Optional check in unary.rs routes delete compilation through this path.

Example (before fix)

let o = {a: {b: 1}};
delete o?.a.b; // returns true but o.a.b is still 1

Example (after fix)

let o = {a: {b: 1}};
delete o?.a.b; // returns true and o.a.b is undefined

Closes #4719

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,862	52,862	0
Passed	49,505	49,497	-8
Ignored	2,261	2,261	0
Failed	1,096	1,104	+8
Panics	0	0	0
Conformance	93.65%	93.63%	-0.02%

Fixed tests (1):

test/built-ins/RegExp/named-groups/non-unicode-property-names-valid.js (previously Ignored)

Broken tests (8):

test/built-ins/RegExp/prototype/exec/regexp-builtin-exec-v-u-flag.js (previously Passed)
test/built-ins/String/prototype/replace/regexp-prototype-replace-v-u-flag.js (previously Passed)
test/built-ins/String/prototype/matchAll/regexp-prototype-matchAll-v-u-flag.js (previously Passed)
test/built-ins/String/prototype/search/regexp-prototype-search-v-u-flag.js (previously Passed)
test/built-ins/String/prototype/search/regexp-prototype-search-v-flag.js (previously Passed)
test/built-ins/String/prototype/match/regexp-prototype-match-v-u-flag.js (previously Passed)
test/staging/sm/RegExp/unicode-raw.js (previously Passed)
test/staging/sm/RegExp/unicode-class-raw.js (previously Passed)

[nekevss]

This is looking pretty good overall.

Can there be a few unit tests added to test the behavior of this PR.

[codecov]

Codecov Report

❌ Patch coverage is 87.27273% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.24%. Comparing base (6ddc2b4) to head (5496d5c).
⚠️ Report is 702 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/bytecompiler/mod.rs	86.79%	7 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4720       +/-   ##
===========================================
+ Coverage   47.24%   57.24%   +10.00%     
===========================================
  Files         476      552       +76     
  Lines       46892    60549    +13657     
===========================================
+ Hits        22154    34662    +12508     
- Misses      24738    25887     +1149     

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[Ansh-699]

okie i'll add in a bit

[jedel1043]

Tests look kinda good, but instead of asserting that the value is undefined I'd use Object.getOwnPropertyDescriptor to assert that the descriptor itself gets deleted. This ensures we're properly checking deletion.

[Ansh-699]

okay