fix: Use shallow copy before reversing

[BeiChenStanly]

Fixes #140.

Problem
getManimClassAtCursor directly calls reverse() on the array returned from findAllIn, which modifies the cached array. This causes the array order to change after the first call, leading to incorrect results on subsequent calls.

Fix
Replace manimClasses.reverse().find(...) with manimClasses.slice().reverse().find(...).

• slice() creates a shallow copy of the original array.
• The reversal is applied to the copy, leaving the cached array unchanged.
• The find operation works on the temporary copy, preserving the original order for future calls.

[Splines]

Nice, thanks for the fix! I will have to fix the GitHub Actions pipeline first, currently it fails with this error.