Added live value and signal descriptor fetching

Live values are stored in the core and their fetch is relatively cheap
as it only requires locking the core live values lock

Signal descriptors are a much heavier call as they query the connector
registry and trigger an O(n) search throughout the different endpoints,
this method is not meant to be used heavily as it requires locking
multiple locks and handling alot of data, this method is meant to be
called once to retreive a list of signal descriptors that the user can
then store and use to reference values against in their frontend code

test/manual/core.py

@@ -23,6 +23,8 @@ dl_core.start()
 try:
     while True:
         dl_core.wait(1)
+        values = dl_core.get_all_live_values()
+        log.debug(f"Core values: {values}")
 except KeyboardInterrupt:
     log.info("Received keyboard interrupt")
     dl_core.stop()