Add function to invalidate xys past critical beta

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 30.16%. Comparing base (8119695) to head (88866c4).

Files	Patch %	Lines
hexrd/xrdutil/phutil.py	0.00%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #668 +/- ## ========================================== - Coverage 30.17% 30.16% -0.01% ========================================== Files 139 139 Lines 22546 22551 +5 ========================================== Hits 6803 6803 - Misses 15743 15748 +5 ```

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