Add active binding for observable_regex

[RasmusSkytte]

Intent

Fixes #201

Approach

N/A

Known issues

N/A

Checklist

• The PR passes all local unit tests
• I have documented any new features introduced
• If the PR adds a new feature, please add an entry in NEWS.md
• A reviewer is assigned to this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.51%. Comparing base (a87b82c) to head (aa2b25b).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #204   +/-   ##
=======================================
  Coverage   88.51%   88.51%           
=======================================
  Files          18       18           
  Lines        1202     1202           
=======================================
  Hits         1064     1064           
  Misses        138      138           

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