locks: add process-wide lock hold time tracking

TrackedMutex and TrackedRwLock wrappers that record hold durations
by source location using #[track_caller]. Stats written to
~/.consciousness/lock-stats.json every second, sorted by max hold time.

Re-exported as crate::Mutex so all locks are instrumented. To disable,
swap the re-export back to tokio::sync::Mutex.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/lib.rs

@@ -1,3 +1,5 @@
+#![feature(async_fn_track_caller)]
+
 // consciousness — unified crate for memory, agents, and subconscious processes
 //
 // thought/       — shared cognitive substrate (tools, context, memory ops)
@@ -47,6 +49,16 @@ pub mod session;
 // Shared utilities
 pub mod util;
 
+// Lock hold time tracking
+pub mod locks;
+
+// Re-export tracked locks as the default — swap to tokio::sync to disable tracking
+pub use locks::TrackedMutex as Mutex;
+pub use locks::TrackedMutexGuard as MutexGuard;
+pub use locks::TrackedRwLock as RwLock;
+pub use locks::TrackedRwLockReadGuard as RwLockReadGuard;
+pub use locks::TrackedRwLockWriteGuard as RwLockWriteGuard;
+
 // CLI handlers
 pub mod cli;