FEAT: Add Kepler Optimization Algorithm (KOA)

[elifgungen]

📑 Description

This PR adds the Kepler Optimization Algorithm (KOA) to Mealpy.

Changes included:

• Added KOA implementation: mealpy/physics_based/KOA.py
• Exported KOA from mealpy/__init__.py
• Added KOA to Sphinx docs: docs/source/pages/models/mealpy.physics_based.rst
• Added KOA entry under Unreleased in ChangeLog.md
• Added a quick smoke test: tests/physics_based/test_KOA.py
• Updated .gitignore to exclude local experiment artifacts (PDF/CSV/MEX and local experiment scripts)

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

Testing performed locally:

• python -m compileall mealpy (success)
• pytest -q (399 tests passed; only a deprecation warning)
• make html (success; Sphinx warnings exist but appear unrelated to KOA changes)

Notes:

• Installing docs requirements in a shared environment may downgrade some packages; using a dedicated virtual environment for docs is recommended.