Fix for normalize function in thresh_utility.py

[KainRasleafar]

Submissions Basics:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you checked all Issues to tie the PR to a specific one?
  Yes – fixes #12

Type of Change:

• Bug fix
• New feature
• Documentation update

All Submissions Cores:

• Have you added an explanation of what your changes do and why you'd like us to include them?
  Yes. This PR improves the normalize function to ensure the output is strictly clipped to the [0, 1] range. This prevents unexpected behavior when input values fall outside the defined min_val/max_val bounds.
• Have you written new unit tests for your changes?
  No new tests added yet – existing usage will benefit from safer behavior, but tests could be extended in a separate PR if needed.
• Do all new and existing unit tests pass locally?

New Thresholder Submissions:

• Have you created a .py in ~/pythresh/thresholds/?
• Have you created a _example.py in ~/examples/?
• Have you created a test_.py in ~/pythresh/test/?
• Have you lint your code locally prior to submission?
• Have you added a reference of the new thresholder in your explanation?