Add ability to subscribe to user state changes

[bsneed]

• added subscribeToUserInfo(handler) -> id.
• added unsubscribe(id).
• added settings entry for autoInstrumentation.
• made public some logging methods.
• added test suite.

[codecov]

Codecov Report

❌ Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.01%. Comparing base (34d55c8) to head (fdbd9af).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/Segment/Utilities/Logging.swift	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #402      +/-   ##
==========================================
- Coverage   71.01%   71.01%   -0.01%     
==========================================
  Files          49       49              
  Lines        4920     4930      +10     
==========================================
+ Hits         3494     3501       +7     
- Misses       1426     1429       +3     

Files with missing lines	Coverage Δ
Sources/Segment/Analytics.swift	84.03% <100.00%> (-0.54%)	⬇️
Sources/Segment/Settings.swift	59.71% <100.00%> (+0.58%)	⬆️
Sources/Segment/State.swift	97.35% <ø> (ø)
Sources/Segment/Utilities/Logging.swift	27.27% <33.33%> (ø)

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