Update employee.py

[MIGithubSE]

Currently, the Employee class accepts first, last, and pay parameters without any validation, potentially leading to invalid or inconsistent employee data. Implementing validation checks for these inputs will enhance the robustness and reliability of the class.

Proposed Changes:

Validate the first and last name inputs to ensure they are not empty and are of type str.
Ensure that the pay attribute is a positive number and of type int or float.

[MIGithubSE]

Validated the first and last name inputs to ensure they are not empty and are of type str. Ensured that the pay attribute is a positive number and of type int or float.