Add Rust-level tests for Promise.all and Promise.any

[mrhapile]

This PR adds Rust-level unit tests for Promise combinators.

Currently core/engine/src/builtins/promise/tests.rs only contains a
basic Promise test and does not cover combinators such as Promise.all
or Promise.any.

While these behaviors are validated through test262, localized Rust
tests improve debugging, provide faster CI feedback, and help prevent
regressions when modifying the Promise implementation.

This PR introduces tests for:

• Promise.all resolution behavior
• Promise.all rejection propagation
• Promise.any first-success resolution

No runtime behavior is modified. This change only adds tests.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,666	49,666	0
Ignored	2,284	2,284	0
Failed	1,013	1,013	0
Panics	0	0	0
Conformance	93.77%	93.77%	0.00%

Tested main commit: 5cbf23323e1be945022cd1e6332cbacc22e9a2c8
Tested PR commit: c0624ca2ea636db4ceb5e162cba56d3866c70895
Compare commits: 5cbf233...c0624ca

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.39%. Comparing base (6ddc2b4) to head (c0624ca).
⚠️ Report is 759 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4882       +/-   ##
===========================================
+ Coverage   47.24%   57.39%   +10.14%     
===========================================
  Files         476      555       +79     
  Lines       46892    60599    +13707     
===========================================
+ Hits        22154    34778    +12624     
- Misses      24738    25821     +1083     

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[jedel1043]

Thanks!