added Luacheck GitHub action (#210)

* added shields.io elements
* #209 luacheck action
* #209 cleanup to pass luacheck
* added check statuses to readme

coordinator/apisessions.lua

@@ -1,11 +1,13 @@
 local apisessions = {}
 
 ---@param packet capi_frame
+---@diagnostic disable-next-line: unused-local
 function apisessions.handle_packet(packet)
 end
 
 -- attempt to identify which session's watchdog timer fired
 ---@param timer_event number
+---@diagnostic disable-next-line: unused-local
 function apisessions.check_all_watchdogs(timer_event)
 end