feat: Add QUERY method (RFC 10008) support

Currently, `gleam_http` defines HTTP methods based on [RFC 2616](https://datatracker.ietf.org/doc/html/rfc2616) and [RFC 5789](https://datatracker.ietf.org/doc/html/rfc5789). However, in June 2026, the IETF published [RFC 10008](https://www.rfc-editor.org/rfc/rfc10008.html) which officially standardizes the `QUERY` method.

The `QUERY` method is designed for safe, idempotent requests that carry a request payload (body) but do not modify server state. It fills the gap between:
- `GET` — safe and cacheable but doesn't support request bodies (per spec)
- `POST` — supports request bodies but is neither safe, idempotent, nor cacheable

**Proposal:** Add `Query` variant to the `Method` type.

If this gets approved, I'd be happy to submit a PR with the implementation, tests, and documentation! 🚀

Start by locating the `Method` type in gleam_http and reviewing how existing RFC 2616 and RFC 5789 methods are represented and tested. Add coverage for the proposed `Query` variant and update the relevant documentation; done means the method is represented consistently and the tests pass.

Written by the indexing model from the issue text.