feat!: replace msgpack with protobuf for all NATS messages

BREAKING CHANGE: All NATS message serialization now uses Protocol Buffers.
- Added proto/messages/v1/messages.proto with 22 message types
- Generated Go code at gen/messagespb/
- messages/ package now exports type aliases to proto types
- natsutil.Publish/Request/Decode use proto.Marshal/Unmarshal
- Removed legacy MessageHandler, OnMessage, wrapMapHandler
- TypedMessageHandler now returns (proto.Message, error)
- EffectiveQuery is now a free function: messages.EffectiveQuery(req)
- Removed msgpack dependency entirely

buf.gen.yaml

@@ -0,0 +1,10 @@
+version: v2
+managed:
+  enabled: true
+  override:
+    - file_option: go_package_prefix
+      value: git.daviestechlabs.io/daviestechlabs/handler-base/gen
+plugins:
+  - protoc_builtin: go
+    out: gen
+    opt: paths=source_relative