Clean up types and drop an unused variable

[akaihola]

Fixes #1174

• Variable added_fnames in cmd_add was only modified, never read
• expand_subdir() yielded both Paths and strs. There are now a bit of hints which I used to verify with Mypy that the types are correct. I also managed to avoid some back-and-forth str<->Path conversions by changing which ones are stored in some variables.
• correct type(...) == <SomeClass> to type(...) is <SomeClass>
• use raw strings when the string contains backslashes (r"\windows\__init__.py") so Python doesn't try to interpret \w as a control character

[paul-gauthier]

Thanks for your interest in aider. I'm not currently looking to add types to this codebase. So it's tricky and time consuming for me to review a PR with all sorts of type annotations.

[akaihola]

Thanks for your interest in aider. I'm not currently looking to add types to this codebase. So it's tricky and time consuming for me to review a PR with all sorts of type annotations.

Fair enough, I now reverted the addition of type hints in this PR.

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(Regarding type annotations, #1217 (Gradual typing) would remove the need to review type annotations by running Mypy to check them automatically – also the Mypy configuration in #1217 is such a minimal one that the current code base passes the check with virtually no modifications.)

[paul-gauthier]

Thanks for this. Nice cleanups.