feat(feature-activation): automatically enable support in MUST_SIGNAL

[glevco]

Depends on #962

Motivation

For updated nodes, when a feature reaches the MUST_SIGNAL phase, the node will automatically enable the feature's bit signaling, unless explicitly removed via the CLI or Sysctl tools.

Acceptance Criteria

• Add BitSignalingService.on_must_signal().
• Update FeatureService to call on_must_signal().

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.10%. Comparing base (f76b6b4) to head (9efd25e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #963      +/-   ##
==========================================
+ Coverage   85.04%   85.10%   +0.06%     
==========================================
  Files         296      296              
  Lines       22918    22925       +7     
  Branches     3451     3452       +1     
==========================================
+ Hits        19491    19511      +20     
+ Misses       2740     2728      -12     
+ Partials      687      686       -1     

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The base branch was changed.