Added testing framework for .osi file validation and GUI input mimicry

[lakshanashreee]

This PR introduces a structured test framework for validating .osi files used in Osdag modules. It includes:

• Pytest-based validation of .osi key fields for the Tension Member – Bolted to End Gusset module.
• Lightweight mock test to precheck tension member .osi values.
• Simulates GUI input collection for Fin Plate Connection and tests compatibility with Osdag design logic.
• Helper script to extract and verify values from .osi files.

Also includes a comprehensive README.md detailing purpose, usage, and structure of the test files.
This lays the foundation for automating .osi validation and GUI input testing across modules.