⚡ Optimize SQLManager.getMainMedal with JOIN query

[google-labs-jules]

💡 What:

• Optimized SQLManager.getMainMedal to use a single SQL INNER JOIN query instead of two sequential queries.
• Refactored SQLManager to allow dependency injection of the Connection object, making it testable.
• Added a new test class SQLManagerTest using JUnit 5 and Mockito to verify the behavior.

🎯 Why:

• The previous implementation performed two database queries to retrieve the main medal for a player: first to get the medal_id from player_main_medal, and then to get the medal details from medal.
• This optimization reduces the number of database round-trips from 2 to 1, improving performance, especially under high load or latency.

📊 Measured Improvement:

• A baseline test confirmed the original implementation executed prepareStatement twice.
• The optimized implementation was verified by SQLManagerTest to execute prepareStatement only once while returning the correct Medal object.
• Note: The build environment had issues resolving PlaceholderAPI dependency. A temporary stub was used to run and verify the tests, which has been removed in the final submission to preserve project integrity. The submitted code assumes a working build environment where PlaceholderAPI is available.

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PR created automatically by Jules for task 13960138847256864281 started by @acsoto

[google-labs-jules]

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