Use tracing JIT to prevent performance test crashes

[WalterWoshid]

The performance workflow could crash during PHPUnit data-provider discovery when setup-php's default opcache.jit=1235 compiled the exporter's recursive helper. Select tracing JIT explicitly while keeping OPcache and JIT enabled for the benchmarks.

Verify the active JIT configuration before testing, allow all PHP 8.1–8.5 matrix jobs to finish independently, and limit each job to 15 minutes. Add PERFORMANCE.md with the debugger findings, local benchmark settings, and the scope of the PHP engine workaround; link it from the README.

Fixes #92.

Validation on the same commit, cf24e3f:

• Fork PHP Tests: three successful attempts, five PHP versions each.
• Fork PHP Performance Tests: three successful attempts, five PHP versions each.
• All 30 matrix jobs succeeded. The existing incomplete/skipped tests and dependency deprecation notices remain.

This addresses the observed test-workflow crash. The underlying PHP compiler defect remains separate, and the library continues to use the application's PHP configuration.