Http Inspector Fast Fail On Non Http Binary Traffic

Fixed a hang in the http_inspector listener filter when BalsaParser was selected (the default since #44679, introduced by #37002). Because BalsaParser defers method-token validation until a line terminator is observed, non-HTTP binary traffic that never sends \n (e.g. Java RMI/JRMP) would cause the filter to buffer up to 64 KiB before closing, stalling the connection for the duration of the downstream timeout. The filter now validates the request-line prefix against the RFC 7230 §3.2.6 token character set before delegating to the parser, restoring the fast-fail behavior the legacy http_parser provided. This behavior can be temporarily reverted by setting the runtime flag envoy.reloadable_features.http_inspector_fast_fail_invalid_method_bytes to false.