feat: deprecate roots, sampling, and logging (SEP-2577) (#884)

SEP-2577 deprecates the Roots, Sampling, and Logging features. The
deprecation is advisory: the features stay fully functional and there is
no wire-level change. Mark the corresponding Rust APIs as deprecated so
downstream users get compiler warnings and migration guidance.

- Forward attributes through the service `method!` macros and deprecate
  `Peer::create_message`, `Peer::list_roots`, `Peer::set_level`, and
  `Peer::notify_logging_message`.
- Forward per-field attributes through the capability `builder!` macro and
  deprecate the generated `enable_roots`, `enable_sampling`, and
  `enable_logging` builders, plus the hand-written
  `enable_roots_list_changed`, `enable_sampling_tools`, and
  `enable_sampling_context`.
- Document the deprecation on the capability types and fields, and in the
  README feature sections.
- Allow `deprecated` at the crate's own call sites so the build stays
  warning-clean, and refresh the message schema snapshots.

examples/servers/src/sampling_stdio.rs

@@ -1,3 +1,4 @@
+#![allow(deprecated)]
 use std::sync::Arc;
 
 use anyhow::Result;