hscontrol/poll: use sub-logger pattern for mapSession

Replace the helper functions (logf, infof, tracef, errf) with a
zerolog sub-logger initialized in newMapSession(). The sub-logger
is pre-populated with session context (component, node, omitPeers,
stream) eliminating repeated field calls throughout the code.

Changes:
- Add log field to mapSession struct
- Initialize sub-logger with EmbedObject(node) and request context
- Remove logf/infof/tracef/errf helper functions
- Update all callers to use m.log.Level().Caller()... pattern
- Update noise.go to use sess.log instead of sess.tracef

This reduces code by ~20 lines and eliminates ~15 repeated field
calls per log statement.

hscontrol/noise.go

@@ -218,7 +218,7 @@ func (ns *noiseServer) NoisePollNetMapHandler(
 	ns.nodeKey = nv.NodeKey()
 
 	sess := ns.headscale.newMapSession(req.Context(), mapRequest, writer, nv.AsStruct())
-	sess.tracef("a node sending a MapRequest with Noise protocol")
+	sess.log.Trace().Caller().Msg("a node sending a MapRequest with Noise protocol")
 	if !sess.isStreaming() {
 		sess.serve()
 	} else {