refactor: split crdt_state.rs into 6 sub-modules with co-located tests
The 2122-line crdt_state.rs is split into a sub-module directory:
- types.rs: CRDT/view types + CrdtEvent (247 lines)
- state.rs: CrdtState struct, statics, init, apply_and_persist (531 lines)
- ops.rs: sync API + apply_remote_op + delta-sync tests (455 lines)
- write.rs: write_item + bug_511 test (273 lines)
- read.rs: read API + dump + dep helpers (469 lines)
- presence.rs: node identity + claim API + heartbeat (176 lines)
- mod.rs: doc, sub-module decls, re-exports, hex helper (53 lines)
Tests are co-located with the code they primarily exercise per Rust convention.
No behaviour change. All 26 crdt_state tests pass; full suite green
(2635 tests with --test-threads=1).
dave
23e22ba49c