ci: enable checklocks workflow for specific packages

This turns the checklocks workflow into a real check, and adds
annotations to a few basic packages as a starting point.

Updates #12625

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I2b0185bae05a843b5257980fc6bde732b1bdd93f

net/stun/stuntest/stuntest.go

@@ -21,8 +21,10 @@ import (
 )
 
 type stunStats struct {
-	mu       sync.Mutex
+	mu sync.Mutex
+	// +checklocks:mu
 	readIPv4 int
+	// +checklocks:mu
 	readIPv6 int
 }
 

net/wsconn/wsconn.go

@@ -105,7 +105,11 @@ type netConn struct {
 	afterReadDeadline atomic.Bool
 
 	readMu sync.Mutex
-	eofed  bool
+	// eofed is true if the reader should return io.EOF from the Read call.
+	//
+	// +checklocks:readMu
+	eofed bool
+	// +checklocks:readMu
 	reader io.Reader
 }