Additional discipline mastery condition

After reaching Grade A, it could be a good idea to complete the grade (i.e. master the discipline) in one of two ways:
* Collect X more XP points (currently implemented, same as other grades)
* Achieve N podium finishes

Possibly, we may want this behavior to be toggle-able in Settings - but then again, maybe this is actually too granular a control to be useful for real players.

The issue describes adding a new mastery condition for a discipline after reaching Grade A, involving either collecting more XP or achieving podium finishes. Look for the code that handles grade progression and discipline mastery, likely in files related to career logic or player progression. Understand how XP and podium finishes are currently tracked. Determine where to add the new condition and any UI changes for a potential settings toggle. Testing will involve verifying the new mastery logic works correctly in the career mode.

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