edge-bench-rs: file stems and subject remainders by hand, mimalloc

The suffix and remainder regexes were most of a new file's description
(333k on boneless 2026): now plain byte matching, with the regex versions
kept as the reference in a test of tricky names and subjects. mimalloc
for the many small strings. Boneless 2026: 360k -> 495k headers/s;
check.ts still finds the outputs identical on all three captures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/edge-bench-rs/Cargo.toml

@@ -9,6 +9,7 @@ base64 = "0.22"
 chrono = "0.4"
 flate2 = { version = "1", default-features = false, features = ["zlib-rs"] }
 md-5 = "0.10"
+mimalloc = "0.1.52"
 regex = "1"
 rustc-hash = "2"
 sha1 = "0.10"