fix: allow regex metacharacters in arguments

[tomholford]

Summary

The argument token's regex only allowed [a-zA-Z\-_+.\\\/*:$0-9@], so path_regexp-style matchers containing (, ), [, ], |, ?, or ^ produced an ERROR node that swallowed everything after the first metacharacter — breaking both parsing and downstream syntax highlighting for the rest of the file.

Repro:

example.com {
    @broken path_regexp /foo/(bar|baz).*
    @also-broken path_regexp /foo/[0-9]+

    handle /xyz {
        file_server
    }
}

Before this change the whole file after @broken falls into an ERROR node.

Fix

Widen the unquoted-argument character classes to include ()[]|?^ so regex arguments lex as a single argument token and the rest of the file parses cleanly. = was intentionally left out to preserve status_code_fallback (=404) precedence.

Test plan

• New path_regexp with Regex corpus case in test/corpus/named_matchers.txt
• tree-sitter test — 43/43 passing (was 42 before)
• Existing Status Code Fallback test still passes
• All examples/*.caddyfile still parse without new errors

Context

Originally surfaced via a downstream Zed extension bug report: nusnewob/caddyfile-zed#7