fix(jsproxy): convert panics to EngineError::Panic using js_expect

[KaustubhOG]

Part of #3241

Converts all 13 panics in jsproxy.rs to EngineError::Panic using
js_expect introduced in #4828.

build() and build_revocable() return types changed from JsProxy/
JsRevocableProxy to JsResult<JsProxy>/JsResult<JsRevocableProxy>.
Checked for external callers —> only a type re-export in mod.rs, so
the cascade is limited to 1 file.

Note: The two JsNativeError::typ() usages in from_object() and
TryFromJs are intentionally left unchanged (becauze i think these are correct
user-facing TypeErrors, not internal implementation failures.)

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,862	52,862	0
Passed	49,627	49,627	0
Ignored	2,263	2,263	0
Failed	972	972	0
Panics	0	0	0
Conformance	93.88%	93.88%	0.00%

Tested PR commit: 7605f9f090ea4c5fb8405946bd2f329c466b20d3

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.13%. Comparing base (6ddc2b4) to head (7605f9f).
⚠️ Report is 756 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/object/builtins/jsproxy.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4854      +/-   ##
==========================================
+ Coverage   47.24%   57.13%   +9.89%     
==========================================
  Files         476      554      +78     
  Lines       46892    60467   +13575     
==========================================
+ Hits        22154    34550   +12396     
- Misses      24738    25917    +1179     

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