Trivial functions optimizations

[hansl]

3 optimizations:

---

Inline immediately invoked function expressions (IIFEs) at compile time,
eliminating function object allocation, call frame creation, and
environment setup overhead. Supports arrow functions and function
expressions with simple parameters, handling expression bodies,
void/side-effect bodies (no return), and bodies with a trailing return.

---

Skip frame creation for empty functions (e.g., function f() {}) by
detecting them at compile time and using CallValue::Complete at runtime,
similar to native function calls.

---

Skip frame creation for empty constructors (e.g., function Foo() {})
that have no fields or private methods and are not derived. Creates the
object and returns it directly via CallValue::Complete, avoiding the
full frame push/pop cycle.

---

This brings the call.js benchmark to within 1.9x of QuickJS:

Benchmark 1: ./target/release/boa /Users/hansl/call.js
  Time (mean ± σ):     578.9 ms ±   1.8 ms    [User: 570.3 ms, System: 4.7 ms]
  Range (min … max):   577.2 ms … 583.3 ms    10 runs

Benchmark 2: qjs /Users/hansl/call.js
  Time (mean ± σ):     307.6 ms ±   0.3 ms    [User: 304.1 ms, System: 2.2 ms]
  Range (min … max):   307.1 ms … 308.1 ms    10 runs

Summary
  qjs /Users/hansl/call.js ran
    1.88 ± 0.01 times faster than ./target/release/boa /Users/hansl/call.js

[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: 34ca7f1f404c2712d6897c3e39e5f5e981ce9ed6
Tested PR commit: 823dbde37ef5d718f9ea8ab626c936b803af6979
Compare commits: 34ca7f1...823dbde

[codecov]

Codecov Report

❌ Patch coverage is 78.70370% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.05%. Comparing base (6ddc2b4) to head (823dbde).
⚠️ Report is 779 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/bytecompiler/inline.rs	72.61%	46 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4918       +/-   ##
===========================================
+ Coverage   47.24%   58.05%   +10.80%     
===========================================
  Files         476      558       +82     
  Lines       46892    61174    +14282     
===========================================
+ Hits        22154    35514    +13360     
- Misses      24738    25660      +922     

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