Apply strict mypy error code

We have been encountering `UnboundLocalError`, which can arise from various pieces of code. To address this issue, let’s configure mypy to identify instances of undefined local variable errors and rectify the affected code.
For more details, refer to the documentation here: [https://mypy.readthedocs.io/en/stable/error_code_list2.html#warn-about-variables-that-are-defined-only-in-some-execution-paths-possibly-undefined](https://mypy.readthedocs.io/en/stable/error_code_list2.html#warn-about-variables-that-are-defined-only-in-some-execution-paths-possibly-undefined).

JIRA Issue: BA-1780