feat(libmsg): extract pymsg-compatible messaging library as shared lib

- Add libmsg: C++20 header-only pymsg protocol implementation
  - Msg.hpp: pmsg_send/pmsg_recv (blocking + deadline modes) + MsgClient
  - MsgServer.hpp: multi-client TCP server with select event loop + thread pool
  - AsyncQueue<T>: generic async batch processing queue
  - RpcClient/RpcServer: JSON RPC convention layer (requires boost::json)
  - Msg_Basic.hpp/cpp: exception hierarchy, constants, version
- Fix thread safety: MsgClient _sockfd/_running use std::atomic with exchange()
- Fix deadline recv: client call() uses shared deadline for header+payload
- Fix graceful shutdown: thread pool drains queued tasks before exit
- Fix pmsg_send size check: enforce 64MiB limit (was 4GiB no-op check)
- Align AsyncQueue batch semantics with Python: batch_size is threshold
- Refactor gateway/LogC.hpp to use libmsg AsyncQueue<T>
- Update gateway Makefile to link -lus_msg, DbC.hpp to use <us/Msg.hpp>
- Add libmsg to _inst.sh build order

gateway/Makefile

@@ -1,10 +1,10 @@
-VERSION := 0.0.1
+VERSION := 0.8.0
 APP_NAME := gateway
 INSTL_DIR := /usr/local/bin
 CPP := g++
-INCS := -I inc/
-MY_LIBS := -L/usr/lib -lus_http -lus_httpclient -lus_crypt
-LIBS := -pthread -lcurl -lssl -lsqlite3 -lz -lcrypto -lboost_json -lboost_program_options
+INCS := -I inc/ -I ../libmsg/inc
+MY_LIBS := -L/usr/lib -L../libmsg/build -lus_http -lus_httpclient -lus_crypt -lus_msg
+LIBS := -pthread -lcurl -lssl -lsqlite3 -lz -lcrypto -lboost_json -lboost_program_options -Wl,-rpath,$(shell cd ../libmsg/build && pwd)
 CPPFLAGS := --std=c++20 -pipe -pthread # -Wall -Werror
 BUILD_DIR = build
 $(shell mkdir -p $(BUILD_DIR))
@@ -13,7 +13,7 @@ $(shell mkdir -p $(BUILD_DIR))
 all: $(BUILD_DIR)/$(APP_NAME).out
 $(BUILD_DIR)/$(APP_NAME).out:	$(BUILD_DIR)/main.o
 	$(CPP) $^ $(LIBS) $(MY_LIBS) -o $@
-$(BUILD_DIR)/main.o:	src/main.cpp
-	$(CPP) $(CPPFLAGS) -c $^ $(INCS) -o $@
+$(BUILD_DIR)/main.o:	src/main.cpp inc/DbC.hpp inc/LogC.hpp inc/Conf.hpp inc/ExpBase.hpp inc/LocalTime.hpp
+	$(CPP) $(CPPFLAGS) -c $< $(INCS) -o $@
 clear:
 	@rm -rvf build/