Unfold HTTP field continuations before validating handshake responses
and matching custom subprotocol offers. Preserve the raw response
returned to callers and reject invalid folded suffixes and duplicate
singleton fields.

Trim server-side protocol whitespace with byte scans before token
validation to avoid quadratic regex backtracking on malformed members.

Add folded-header compatibility and long-whitespace regressions.
All nine test files pass 1030 tests on OpenResty 1.31.8.1. Independent
boundary probes and real TCP performance checks also pass.