fixed crop_frames for robustness

[keeminlee]

• Adds crop_frames utility for flexible frame subsetting using 1-based (start, end) tuples with optional open-ended bounds (None).
• Implements strict input validation (no overlaps, out-of-bounds, or invalid types) and consistent NumPy slicing semantics.
• Includes unit tests verifying correct cropping, open-ended behavior, and error handling for invalid inputs.

[themattinthehatt]

let's make the ranges match how python would process, i.e. 0-based, left-inclusive, right-exclusive