FIX-#7138: Stop reloading modules for custom docstrings.

[sfc-gh-mvashishtha]

Signed-off-by: sfc-gh-mvashishtha mahesh.vashishtha@snowflake.com

What do these changes do?

Stop reloading modules for custom docstrings. See #7138 for motivation.

• first commit message and PR title follow format outlined here

  NOTE: If you edit the PR title to match this format, you need to add another commit (even if it's empty) or amend your last commit for the CI job that checks the PR title to pick up the new PR title.

• passes flake8 modin/ asv_bench/benchmarks scripts/doc_checker.py
• passes black --check modin/ asv_bench/benchmarks scripts/doc_checker.py
• signed commit with git commit -s
• Resolves BUG: using docstring extensions causes several incorrect behaviors because DataFrame, Series, and BasePandasDataset cannot recognize each other #7138
• tests added and passing
• module layout described at docs/development/architecture.rst is up-to-date

[anmyachev]

LGTM!

[noloerino]

LGTM, thanks!