Update BadPixels with new bits

[philsmt]

Some updates to the BadPixels enum as discussed in CAL dev team:

• EXPERT_CHOICE for interactive masks set by the operators and experts, e.g. the BadPixelsManual
• Reserved last two bits for arbitrary use labelled USER1 and USER2

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.40%. Comparing base (e84e4c1) to head (7a1248a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #519      +/-   ##
==========================================
+ Coverage   75.39%   75.40%   +0.01%     
==========================================
  Files          39       39              
  Lines        7182     7185       +3     
==========================================
+ Hits         5415     5418       +3     
  Misses       1767     1767              

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[philsmt]

@takluyver will add the changelog entry directly to #518