Update matrix-sdk to v0.17.0 and Rust toolchain to 1.95.0

matrix-sdk 0.17.0 brings a few breaking API changes that we adapt to:

- Drop the `native-tls` feature on matrix-sdk; it was removed upstream
  in 2026-04 (matrix-sdk now hardwires rustls). The previous workaround
  comment referencing rust-mxlink issue #1 is no longer relevant.
- `Relation::Reply` is now a tuple variant wrapping a `Reply` struct;
  pattern matches updated to bind through `reply.in_reply_to.event_id`.

Also bumps the Rust toolchain from 1.93.0 to 1.95.0 (closes #85, which
proposed the Dockerfile bump in isolation). rustc 1.94+ trips a
query-depth overflow when computing async layouts in the matrix-sdk
timeline future graph; matrix-rust-sdk PR #6489 raises the limit, but
\`recursion_limit\` is per-crate, so we repeat \`#![recursion_limit = "256"]\`
on this crate root.

Bumps the mxlink floor to 1.14.0, which carries the matching adapter.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
-channel = "1.93.0"
+channel = "1.95.0"
 components = ["rustfmt", "clippy"]
 profile = "default"