syncs: add Mutex/RWMutex alias/wrappers for future mutex debugging

Updates #17852

Change-Id: I477340fb8e40686870e981ade11cd61597c34a20
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/magicsock/endpoint_tracker.go

@@ -6,9 +6,9 @@ package magicsock
 import (
 	"net/netip"
 	"slices"
-	"sync"
 	"time"
 
+	"tailscale.com/syncs"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tempfork/heap"
 	"tailscale.com/util/mak"
@@ -107,7 +107,7 @@ func (eh endpointHeap) Min() *endpointTrackerEntry {
 //
 // See tailscale/tailscale#7877 for more information.
 type endpointTracker struct {
-	mu        sync.Mutex
+	mu        syncs.Mutex
 	endpoints map[netip.Addr]*endpointHeap
 }