Enable pylint for python/taichi folder

Currently if you run pylint python/taichi/ there're a lot of warnings/errors. We'd like to get rid of these and run pylint in CI. Also in .pylintrc we skip a few checkers but it'd be nice to enable some of them back, e.g. import-outside-toplevel.

This work is good for new contributors, and you're welcome to submit one PR per pylint checker/rule.

• singleton comparison (C0121)
• import outside top level (C0415)
• redefined-outer-name (W0621)
• redefined-builtins (W0622)
• consider using from import (R0402)
• use f-string (C0209)
• no-self-use (R0201)
• useless-super-delegation (W0235)
• redefined-outer-name (W0621)
• unused-variable (W0612)
• no-else-return (R1705)
• reimport (W0404)
• unused-import (W0611)
• wildcard-import (W0401)

Reference: https://pylint.pycqa.org/en/latest/technical_reference/features.html