[lint] Fix remaining variables shadowing python builtins and enable detection of shadowed variables going forward

Summary:
This is the last step cleaning up variables shadowing python builtins. Going forward the linter will catch these and report an error.

Depends on D13748, D13749, and D13750

Test Plan:

ninja check-functional

From project root:

flake8 | grep A001

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13751