Add Config, signing functions, passcode saving/deleting, and tests

[kentbull]

Added remaining features for SignifyTS parity for getting agent config, request signing functions, passcode saving and deleting, and tests for all of this.

[codecov]

Codecov Report

❌ Patch coverage is 91.75258% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.58%. Comparing base (532e20d) to head (1fd3d6e).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
src/signify/app/clienting.py	95.52%	3 Missing ⚠️
src/signify/core/keeping.py	62.50%	3 Missing ⚠️
src/signify/app/aiding.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #135      +/-   ##
==========================================
+ Coverage   88.53%   89.58%   +1.05%     
==========================================
  Files          17       20       +3     
  Lines        1064     1469     +405     
==========================================
+ Hits          942     1316     +374     
- Misses        122      153      +31     

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