HTTPCORE-637: RFC 3986 URI: parse/resolve/normalize.

[arturobernalg]

Implements HTTPCORE-637 with a small, immutable RFC 3986 URI value type that preserves raw text and supports resolve/normalize per §§5.2/6. Implementation is table-driven ASCII (no regex/Character) and fixes terminal ./.. trailing-slash behavior (§5.2.4). Host reg-names are lowercased; IPv6 literals preserved. Internal helpers (Ascii, PercentCodec, Ports, DotSegments, UriTokenizer) are marked @Internal and stateless. Removes the unused Rfc3986UriBuilder. Test suite includes the RFC resolution matrix and edge cases; all pass.