Bound compiled dynamic route regex chunks

[samuelpatro]

A dynamic bucket with 2,000 routes sharing a prefix exceeds PCRE's compiled-regex limit. Both hits and misses then scan routes sequentially on every match.

Compile each bucket into ordered chunks bounded by 100 routes and approximately 8 KB of pattern source. Matching still chooses the earliest sorted candidate across the specific and catch-all buckets; wildcard precedence, expression/condition rejection, and regex-error fallback retain their existing behavior. Compiled cache format version 2 rebuilds old payloads, and malformed chunk shapes are rejected.

Regression tests cover 2,000/5,000-route hit and miss fallback counts, long Unicode patterns, optional parameters, priority/rejection, serialization, and old/malformed cache payloads. The large-bucket test fails on develop (two sequential fallbacks) and passes with the change (zero). Added two 5,000-route benchmark subjects. PHP 8.4 full suite: 234 tests, 1,487 assertions, no failures; one pre-existing risky test has no assertions. PHP syntax and diff checks pass. A single oversized route can still use the existing safe sequential fallback.

Rechecked on 2026-09-18: seven samples of 100 warm matches per sample, PHP 8.4, 5000 same-prefix dynamic routes. Median late hit: develop 2.110 ms, PR 0.096 ms (~22x faster); miss: 2.048 ms to 0.073 ms (~28x faster). Sequential fallback count drops from one per match to zero. At 100 routes, late-hit timing is effectively unchanged (2.96 vs 3.01 microseconds). Compilation is excluded. Timings are local illustrations; behavior and fallback counts are the regression gates. Full suite remains 234 tests / 1487 assertions.