[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/observed_write_template.rs

@@ -44,7 +44,7 @@
 //! `Encode` (`.cs:51-64`) writes:
 //!
 //! 1. The captured prefix (`_prefix`, raw bytes) — preserved verbatim.
-//! 2. The freshly-encoded value bytes from [`encode_value`].
+//! 2. The freshly-encoded value bytes from `encode_value_bytes`.
 //! 3. The captured suffix (`_suffixBeforeWriteIndex`) — preserved verbatim.
 //! 4. The fresh `writeIndex` as i32 LE in the trailing 4 bytes.
 //!
@@ -167,12 +167,12 @@ impl ObservedWriteBodyTemplate {
         }
     }
 
-    /// Captured opcode at body[0]. Mirrors `_prefix[0]`.
+    /// Captured opcode at `body[0]`. Mirrors `_prefix[0]`.
     pub fn command(&self) -> u8 {
         self.command
     }
 
-    /// Captured wire-kind byte at body[17]. Drawn from the captured prefix,
+    /// Captured wire-kind byte at `body[17]`. Drawn from the captured prefix,
     /// not from the runtime [`MxValueKind`] (which can disambiguate
     /// String vs DateTime past the encoder collapse).
     pub fn wire_kind(&self) -> u8 {