Process/cleanup: dead PARAMETER_WIDENING flag, orphaned test fixtures, lost golden coverage, PHPStan on 8.5 in CI

[lisachenko]

Summary

Process and hygiene items from the PHP 8.5 support audit (PR #597); user-approved batch.

1. Dead feature flag PARAMETER_WIDENING

src/Aop/Features.php:49-54 gates "parameter widening for PHP>=7.2.0" — unconditional engine behavior for eight years and dead configuration on a ^8.4 floor. The $useParameterWidening/$useTypeWidening plumbing threads through WeavingTransformer, all four proxy generators, InterceptedConstructorGenerator, and MethodGenerator::fromReflection. Remove flag + plumbing (BC note for 4.0 changelog; Features bitmask already has holes at 8/16/32).

2. Orphaned golden fixtures — and lost version coverage

14 of 40 files in tests/Instrument/Transformer/_files/ are referenced by no test (leftovers of the removed SelfValueTransformer and CachingTransformer):

anonymous-class{,-transformed}.php
file-with-self{,-transformed}.php, file-with-self-no-namespace{,-transformed}.php
php80-file{,-transformed}.php
php81-file{,-transformed}.php
php82-file{,-transformed}.php   (input and expected output byte-identical)
yii_style{,_output}.php

Deleting them is not enough: their removal from the test flow silently dropped all golden-file coverage of general PHP 8.0–8.2 syntax through the weaver (only enums, readonly classes, #[\Override], and property hooks survive). Replace with current-pipeline fixtures covering 8.0–8.2 syntax, 8.3 typed constants, and the audited 8.5 constructs (the audit fixtures in tests/Fixtures/audit/src/ are the seed).

3. PHPStan CI runs only on PHP 8.4

.github/workflows/phpstan.yml pins 8.4 while phpunit runs 8.4/8.5(/8.6 experimental). Reflection signatures/semantics differ per version (the 8.5 self/parent resolution change proved it). Add an 8.5 job.

4. Minor

• tests/functions.php glob-hijack helper: add parameter/return types.
• Three hand-rolled "static singleton configured on demand" patterns (FilterInjectorTransformer extract() at :105-109, MagicConstantTransformer statics, SourceTransformingLoader statics) — at minimum replace the extract() with typed reads.
• Constructor property promotion in Instrument/, Core/, Proxy/Generator/ constructors (the Aop/ layer is already promoted) — mechanical, large-diff; fine to defer or do per-file while touching for other reasons.

[lisachenko]

Status after #614 and #617 merged — most of this issue is done:

• Dead PARAMETER_WIDENING flag + $useParameterWidening plumbing removed (Fix attribute-class and new-in-initializer weaving fatals; typed consts, PARAMETER_WIDENING removal #617, BC note in CHANGELOG)
• 12 orphaned fixtures deleted; yii_style* correctly kept — still referenced by FilterInjectorTransformerTest (Fix enum const-expression case values, extend pointcut expressiveness, add PHP 8.5 limitations doc #614)
• Golden coverage of general PHP 8.0–8.3 syntax restored via php80-82-syntax fixture (Fix attribute-class and new-in-initializer weaving fatals; typed consts, PARAMETER_WIDENING removal #617)
• PHPStan CI runs an 8.4 + 8.5 matrix (Fix enum const-expression case values, extend pointcut expressiveness, add PHP 8.5 limitations doc #614)
• tests/functions.php glob override typed (Fix enum const-expression case values, extend pointcut expressiveness, add PHP 8.5 limitations doc #614)
• Constructor property promotion across Instrument/ and Proxy/Generator/ (Fix attribute-class and new-in-initializer weaving fatals; typed consts, PARAMETER_WIDENING removal #617; a few left where fields are derived from other args)

Remaining (this issue stays open for):

• The three hand-rolled "static singleton configured on demand" patterns: FilterInjectorTransformer (extract(self::$options, EXTR_IF_EXISTS) at ~105-109 — replace with typed reads), MagicConstantTransformer statics, SourceTransformingLoader statics
• CachePathManager::__destruct() writing cache files at shutdown (order-of-shutdown fragile; noted during the audit)

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