perf(grep): up to 14.5× speedup via preFilter extensions and matcher reuse

[Hazzng]

Summary

• Anchored alternation preFilter (regex.ts): extractPreFilter now strips leading ^ / trailing $ from each alternative before extracting the literal needle. Patterns like ^def \|^async def (previously unoptimized) now get the String.indexOf fast-path instead of running the full RE2 NFA against every line.
• Matcher reuse extended (user-regex.ts): match(), replace() (both string and callback paths), search(), and matchAll() now route through acquireMatcher(). Previously only test() and exec() used the cached matcher, leaving awk/sed hot-paths allocating a new RE2JS.Matcher on every call.
• Multiline file-level preFilter (matcher.ts): searchContentMultiline() now receives preFilter and performs a whole-file content.includes(needle) check before splitting lines or invoking RE2 — files with no matching needle are rejected in O(n) string scan instead of O(n·m) NFA.
• grep loop preFilter short-circuit (grep.ts): after readFile, a file-level needle check now skips searchContent (and content.split("\n")) entirely for files with no match. Count-only mode (-c) emits 0\n correctly without entering the line loop.

Benchmark results

100 files × 100 lines, 5 runs, median reported. Baseline: just-bash@3.0.1 (npm latest).

Pattern	Before (npm)	After (branch)	Speedup
^def |^async def (anchored BRE — the key case)	139.5 ms	9.6 ms	14.5×
def (simple literal — baseline)	17.6 ms	7.7 ms	2.3×
def |async def (unanchored alternation)	29.9 ms	9.3 ms	3.2×

The baseline itself dropped 2.3× because acquireMatcher now covers match(), search(), and replace() — reducing GC pressure for all regex operations, not just the grep hot path.

Root cause (the ^def \|^async def case)

literalFromAlternative in regex.ts rejected any alternative containing ^ or $, treating them as regex metacharacters. Since ^L implies the line contains L, and L$ implies the line contains L, stripping outer anchors before needle extraction is provably sound (false positives are safe; RE2 re-checks the match). The fix is a 17-line anchor-strip in literalFromAlternative before the existing character loop.

Tests added

File	New tests
src/commands/search-engine/regex.test.ts	anchored single / alternation / mixed-anchor / anchor-only / escaped-anchor cases
src/regex/user-regex.test.ts	acquireMatcher reuse for match, replace (string + callback), search, matchAll, 1000-call state leak check
src/commands/search-engine/matcher.test.ts	multiline preFilter: no-needle early exit, needle-present normal run, invertMatch bypass

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[Hazzng]

@cramforce i've made some code optimization for grep so its getting quite abit faster now compared to the last PR. Can you have a look please ? thanks