Support MoviePy 2 imports

[Mirochill]

Summary:

• keep the MoviePy 1.x moviepy.editor import path when it exists
• fall back to MoviePy 2.x top-level imports when only moviepy.editor is missing
• re-raise other missing-module errors instead of hiding dependency problems

Validation:

• git diff --check
• git diff --cached --check
• git show --check --stat --oneline HEAD
• Not run locally.

Closes #37