Respect predefined modes in get_default_mode

Also make linker and optimizer non-mutable config as the mode is cached after using them for the first time.

Author: ricardoV94

pytensor/compile/mode.py

@@ -535,13 +535,13 @@ def get_mode(orig_string):
         ret = Mode(linker=config.linker, optimizer=config.optimizer)
 
     if orig_string is None:
-        # Build and cache the ~~default~~ first requested mode
         if config.optimizer_excluding:
             ret = ret.excluding(*config.optimizer_excluding.split(":"))
         if config.optimizer_including:
             ret = ret.including(*config.optimizer_including.split(":"))
         if config.optimizer_requiring:
             ret = ret.requiring(*config.optimizer_requiring.split(":"))
+        # Override the cache with the new class mode
         instantiated_default_mode = ret
 
     return ret