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>

Dockerfile

@@ -4,7 +4,7 @@
 #                                     #
 #######################################
 
-FROM docker.io/rust:1.93.1-slim-trixie AS build
+FROM docker.io/rust:1.95.0-slim-trixie AS build
 
 RUN apt-get update && apt-get install -y build-essential pkg-config libssl-dev libsqlite3-dev