perf(semver): build CompilingMatcher's cache key without allocating

CompilingMatcher::match formats `<operator><constraint>;<version>` into a
fresh String on every call, including the cache hits the key exists to serve.
Profiling put the formatting at 2.9 % of self time, more than the match it
guards. Build the key into a reused thread-local buffer and copy it only when
there is a miss to record.

Taking the version as `&str` rather than `String` removes the copy the callers
made for the same reason: `optimize_by_identical_dependencies` allocated one
per candidate package in its innermost loop.

laravel/framework require --no-install (warm cache, network disabled):

  instructions:u  9142799608 -> 8895247586  (-2.7 %)
  cycles:u        4626440169 -> 4496152041  (-2.8 %)
  wall (hyperfine, 25 runs)
                  1.239 s +- 0.014 s -> 1.227 s +- 0.016 s  (-1.0 %)

monolog/monolog is unchanged (102.1 ms -> 101.6 ms, within noise).
composer.lock is byte-identical for both packages.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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