Support plugins defined as inner classes

[alexey-pelykh]

Support referencing the following plugin class by name and by type:

class Outer:
    class MyHttpProxyPlugin(HttpProxyPlugin):
        # ...

[alexey-pelykh]

Hm, I may need some insights on what have failed since:

Unable to find qualified name for module: check.py

tests/test_main.py

is there for me on unmodified develop as well

[abhinavsingh]

Hm, I may need some insights on what have failed since:

Unable to find qualified name for module: check.py

tests/test_main.py

is there for me on unmodified develop as well

Thank you @alexey-pelykh for this PR. These are possibly broken due to updated lint toolkit (in this case flake8 I suppose). At times upstream changes starts to show up as new lint errors in our repo :(. I'll address this in a separate PR and re-run/review this PR sometime morrow. Thanks again.

[abhinavsingh]

@alexey-pelykh I am fixing the lint issues via #1321 , we should be able to get going on this PR thereafter. Meanwhile, could you add a few lines about capabilities that this PR adds to the Loading Plugins section. This will allow others to also discover this magic :) https://github.com/abhinavsingh/proxy.py#loading-plugins

[abhinavsingh]

@alexey-pelykh All looks good. Thank you again for your PR and included tests 🙏. Merging, we can update doc in a separate PR effort.

[abhinavsingh]

LGTM