chore(release): v2.3.0

Bump all workspace crates, the node package and pyproject to 2.3.0, finalize
the changelog and add upgrade notes for the behaviour changes.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

CHANGELOG.md

@@ -1,6 +1,24 @@
 # Changelog
 
-## Unreleased
+## v2.3.0 (2026-09-19)
+
+### Upgrade Notes
+- **A memory store now has a single writer.** `HDF5Memory::create`/`open` take
+  an exclusive lock (`<store>.h5.lock`); a second open of the same store — in
+  the same or another process — returns `MemoryError::Locked`. Code that opened
+  a second handle just to read should use `HDF5Memory::open_read_only`.
+- **Unsigned array attributes arrive as `AttrValue::U64Array`**, not
+  `I64Array`, and `attrs()` may now return `AttrValue::Raw`. Exhaustive matches
+  on `AttrValue` need the two new arms.
+- **WAL header version 3 → 4.** v3 files are read and upgraded in place, but a
+  store written by 2.3.0 with a pending WAL cannot be opened by 2.2.0 or
+  earlier (it is refused, not corrupted). Checkpoint first
+  (`flush_wal`) if you need to downgrade.
+- `MemoryConfig::compression` now uses deflate unless the agent's new `zstd`
+  feature is enabled; it previously failed outright in a default build.
+- `MemoryError` gained `Locked`; `FormatError` gained `UnresolvedSharedMessage`,
+  `ExternalDataFilesUnsupported` and `ExternalLinkUnsupported`; `MessageType`
+  gained `ExternalDataFiles`.
 
 ### Bug Fixes
 - `clawhdf5-format`: compound datatypes written with **default libver bounds**