[technical improvement] make `self._plugin_overrides` a dictionary indexed by func name, for faster access

[giuseppe-coco]

Is your feature request related to a problem? Please describe.
I am browsing through the cat's code and I found a TODO comment that suggest implementing an improvement: self._plugin_overrides = [] # TODO: make this a dictionary indexed by func name, for faster access
in mad_hatter.plugin module.
So I think I developed the improvement.

Is there a quick way to test it using test module ?

[pieroit]

Hi @giuseppe-coco there is a mock_plugin in the test suite that is used to test plugin primitives.
I guess we have no tests yet for the @plugin decorator.

To run them in general, here is a guide:
https://cheshire-cat-ai.github.io/docs/production/administrators/tests/

For sure the improvement is welcome, we'll see how to test it, make the PR if you have pleasure to do it ;)