perf(dicer): avoid regex when parsing headers

[mcollina]

Summary

• avoid regex-based header field parsing in Dicer's HeaderParser
• scan CRLF-delimited header lines directly instead of using buffer.split(/\r\n/g)
• preserve folded-header handling and existing malformed-header behavior

Performance

Local HeaderParser microbenchmark on a 3-header block:

• before: ~1.78M ops/sec
• after: ~2.66M ops/sec

A local @platformatic/flame run also confirmed HeaderParser._parseHeader remains a primary hotspot, but its self-time dropped in the targeted multipart workload.

Validation

• npm test
• npm run lint

[ivan-tymoshenko]

lgtm

[marcopiraccini]

lgtm

[mcollina]

Added a follow-up optimization in 6d81635: HeaderParser now scans for the header terminator directly instead of routing header parsing through StreamSearch. I also added coverage for CRLFCRLF split across chunks, including after maxHeaderSize is reached.\n\nValidation:\n- npm test\n- npm run lint\n- npm run bench:dicer\n- remote CI checks are passing.