perf: ZTS-tax reduction pass - TSRMLS static-cache audit, PGO verification, TLS model

[luthermonson]

The v1 deep-dive (2026-07-07) measured ~5-10% in-PHP ZTS overhead vs NTS php-fpm. Shrink it:

1. Audit ZEND_ENABLE_STATIC_TSRMLS_CACHE=1 is set for php core AND every bundled extension in the spc build (it is confirmed for opcache's config.m4 only).
2. Verify PGO is actually active in the gnu lanes (fork is named -pgo- but confirm the profile-use step runs; if not, wire it - typically 5-10% gain).
3. Experiment: -ftls-model=initial-exec for libphp.a (statically linked into ephpm, so IE is safe for the main binary; measure interaction with dlopen'd extensions).
   Target ships with ephpm v0.4.x (perf release).