Add `__repr__` to `Region` and `CacheMiss` utility classes for better debugging

[Yashsingh045]

Problem

The Region class and CacheMiss exception in malariagen_data/util.py lack informative string representations for debugging.

• Region has a __str__ method (e.g., "2L:100,000-200,000") but no __repr__. When a Region object appears inside a list, dict, or is inspected interactively in Python/Jupyter notebooks, you get the unhelpful default: <malariagen_data.util.Region object at 0x7f...>.

• CacheMiss is a bare Exception subclass (class CacheMiss(Exception): pass) with no default message and no __repr__. When caught and printed during debugging, it shows as CacheMiss() with no context.

Evidence

In malariagen_data/util.py:

• Region class (line ~542): has __str__ but no __repr__
• CacheMiss class (line ~906): class CacheMiss(Exception): pass

Proposed Fix

1. Add __repr__ to Region that returns a valid Python constructor-style string, e.g.:

   • Region('2L', 100000, 200000) → repr shows Region('2L', 100000, 200000)

2. Add __repr__ (and optional default message) to CacheMiss for clearer output during debugging.

Impact

Better debugging experience for both users and developers. Small, targeted change with large UX improvement.

[Yashsingh045]

Hey @jonbrenas ,
I have opened a PR #1220 for this issue.
Could you please review it?