Implement Unit Tests for Medieval Factions Using MockBukkit

[dmccoystephenson]

Goal

Set up a robust unit testing environment for the Medieval Factions plugin using MockBukkit. This will enable testing of core functionality, including player faction applications, without requiring a live Minecraft server.

Acceptance Criteria:

1. MockBukkit is successfully integrated into the project as a test dependency.
2. Unit tests are implemented to simulate a player submitting an application to join a faction.
3. Tests cover the following scenarios:
   • Successful application submission.
   • Failure due to invalid faction name.
   • Failure due to missing application data.
4. Tests run successfully using the JUnit test runner without requiring a live server.
5. Documentation is updated to include setup instructions for running tests.