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/agent/tools/lsp.rs

@@ -123,7 +123,7 @@ fn find_project_root(file_path: &str) -> Option<String> {
 const IDLE_TIMEOUT_SECS: u64 = 600;
 
 use std::sync::OnceLock;
-use tokio::sync::Mutex as TokioMutex;
+use crate::Mutex as TokioMutex;
 
 struct Registry {
     configs: Vec<crate::config::LspServerConfig>,