Add comprehensive tests for critical code paths

[B-BiM]

Why

Add a comprehensive pytest suite to cover the most critical business logic paths: steel connection calculations, beam analysis equations, and wood stud wall design factors. This addresses gaps in automated verification for core calculation and data-mutation logic so regressions are caught early.

What/Approach

• Adds pytest config (pytest.ini) and shared fixtures (tests/conftest.py).
• Adds unit test suites:
  • tests/test_bolt_group.py — Brandt instantaneous center, bolt grid and centroid logic (steel)
  • tests/test_beam_equations.py — polynomial utilities, point-load reactions, shear/moment/deflection (analysis)
  • tests/test_wood_wall.py — wood_stud_wall initialization, factor application, deflection capacity (wood)
• Adds test docs and a detailed coverage report (tests/README.md, TEST_IMPLEMENTATION_SUMMARY.md, TEST_COVERAGE_REPORT.md).

Key decisions and notes

• Focused on business logic (non-GUI). GUI/Tkinter code was intentionally not tested here; tests exercise the underlying calculation classes used by the GUI.
• Tests validate physical correctness (equilibrium, positive capacities, symmetry) in addition to numeric correctness.
• Large/edge-case values and degenerate conditions (e.g., bolt at IC, loads at supports, extreme temperatures) are covered.

How to run

• Install pytest and numpy: pip install pytest numpy pytest-cov
• Run all tests: pytest tests/ -v
• Coverage: pytest tests/ --cov=Analysis --cov=Steel --cov=Wood --cov-report=html

Notes

• Local push to origin failed due to permission (origin not writable from this environment). The pull request flow will create an appropriate upstream branch or fork as needed when creating the PR.

Files changed (summary)

• Added: pytest.ini, tests/{conftest.py,test_bolt_group.py,test_beam_equations.py,test_wood_wall.py,init.py,README.md}, TEST_IMPLEMENTATION_SUMMARY.md, TEST_COVERAGE_REPORT.md

Review guidance

• Focus review on the test assertions for physical validity and the initialization logic in wood_stud_wall; these tests capture the highest-risk code paths.
• If any expected behavior differs from the test assumptions, point it out and the tests can be updated to match the intended domain behavior.