[F42] cargo doc --workspace --no-deps clean (0 warnings)

Fix all 33 rustdoc warnings across the workspace:

- Unresolved intra-doc links: rewrite [`name`] → either backtick text
  (when not actually a link) or fully-qualified `[Type::method]` /
  `[crate::module::name]` form. Affected: mxaccess-codec
  (asb_variant, item_control, metadata_query, observed_write_template,
  reference_handle, write_message), mxaccess-rpc (pdu), mxaccess-nmx
  (client), mxaccess-asb-nettcp (nmf), mxaccess-callback (exporter),
  mxaccess (asb_session, session, lib).
- Bracket-text being interpreted as link refs (e.g. `body[17]` →
  `` `body[17]` ``).
- Private-item references in public docs (CALLBACK_BROADCAST_CAPACITY,
  recover_connection_core, mxvalue_to_writevalue) reduced to
  backtick-text since they aren't part of the public API.

`RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps` now
exits clean. Workspace 759 tests pass; clippy clean.

Defers `#![warn(missing_docs)]` lint to a future pass — the cleanup
target is the broken-link warnings, which are signal; missing-docs
would surface hundreds of low-priority public-item gaps that are out
of scope for this F-number.

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

rust/crates/mxaccess-codec/src/item_control.rs

@@ -2,7 +2,7 @@
 //!
 //! Direct port of `src/MxNativeCodec/NmxItemControlMessage.cs`. The body
 //! carries an advise-supervisory or unadvise command together with a 16-byte
-//! item correlation GUID and a 14-byte projection of an [`MxReferenceHandle`]
+//! item correlation GUID and a 14-byte projection of an [`crate::reference_handle::MxReferenceHandle`]
 //! (handle bytes 6..20 — `object_id` through `attribute_index`).
 //!
 //! ## Wire layout
@@ -87,7 +87,7 @@ const PAYLOAD_LENGTH: usize = 18; // cs:28 — 7×u16 + u32 tail = 18 bytes
 pub const DEFAULT_TAIL: u32 = 3;
 
 /// Decoded NMX item-control body. The fields after `item_correlation_id`
-/// project bytes 6..20 of an [`MxReferenceHandle`] — see
+/// project bytes 6..20 of an [`crate::reference_handle::MxReferenceHandle`] — see
 /// `NmxItemControlMessage.cs:71-81, 134-141`.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct NmxItemControlMessage {