feat: add Python (PyO3) and Ruby (Magnus) native bindings

Introduces three crates:
- quicnprotochat-bindings: shared Rust API returning structured data
  instead of printing to stdout; explicit per-call auth (no global
  OnceLock); QPCE state files fully interoperable with the CLI.
- quicnprotochat-python: PyO3 0.22 extension; GIL released during
  all blocking QUIC calls via py.allow_threads.
- quicnprotochat-ruby: Magnus 0.7 extension; Rakefile build task.

Core/proto crates referenced via git dep on the main repo.

crates/quicnprotochat-ruby/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name        = "quicnprotochat-ruby"
+version     = "0.1.0"
+edition     = "2021"
+description = "Ruby bindings for quicnprotochat (Magnus)."
+license     = "MIT"
+
+[lib]
+name       = "quicnprotochat_ruby"
+crate-type = ["cdylib"]
+
+[dependencies]
+quicnprotochat-bindings = { path = "../quicnprotochat-bindings" }
+magnus = { version = "0.7" }