Fix: Improve validation in _handle_region_coords

[vinitjain2005]

Description:
This PR enhances the validation and error handling in the _handle_region_coords function, ensuring robust parsing of genomic region strings.

Changes Made:

• Implemented strict regex validation for region format (contig:start-end)

• Added type checking for the region input

• Improved error messages for better debugging

• Removed silent failure (None return) and replaced with explicit exceptions

• Added logical validation:

  • Start position must be ≥ 1
  • End position must be ≥ start

• Added validation to ensure the contig exists

• Added boundary checks against contig length

Before vs After:

Before:

• Weak regex validation
• Allowed malformed inputs
• Could return None silently
• Limited error handling

After:

• Strict format validation
• Clear and descriptive error messages
• No silent failures
• Strong input validation

Testing:

• Tested with valid input: "chr1:100-200"

• Tested invalid inputs:

  • "chr1-100-200"
  • "chr1:abc-xyz"
  • "chr1:200-100"

• All invalid cases now raise appropriate exceptions

Impact:
Improves reliability and prevents incorrect genomic region parsing, reducing the risk of downstream errors.

Related Issue:
Closes #1182

Github: @vinitjain2005

[vinitjain2005]

@jonbrenas @tristanpwdennis please verify and merge the issue