Numerous fixes and improvements to the proxy as usual. The proxy now embeds our routelib lua library to make it even easier to use. To use the builtin routelib start the proxy with -o proxy_config=routelib (note lack of .lua) and it will use the version shipped with the binary.

See https://docs.memcached.org/features/proxy/ for more information on using the proxy.

• proxy: fix mutator reserr err messages
• proxy: set result object status from mutator
• proxy: fix compilation issue on beta RHEL/GCC
• proxy: simplify lua GC logic
• proxy: add mcp.luagc_ratio(float)
• proxy: improve various mutator copy steps
• proxy: don't allow mutating mutated objects
• proxy: fix for result value buffers
• proxy: internally track rctx:new objects
• proxy: fixes to request object
• proxy: embed routelib