chore: implement typings in ending module

[lenkan]

As a continuation from #279, I fixed the typings for the end/ending.ts module.

Also split the tests up in to smaller tests to make it easier to follow what the module is doing. In that I added some more test cases that were missing.

[codecov]

Codecov Report

Attention: Patch coverage is 87.03704% with 7 lines in your changes missing coverage. Please review.

Project coverage is 83.84%. Comparing base (5801e63) to head (242c8d9).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/keri/end/ending.ts	86.27%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #280      +/-   ##
==========================================
- Coverage   83.93%   83.84%   -0.10%     
==========================================
  Files          48       48              
  Lines        4257     4258       +1     
  Branches     1051     1057       +6     
==========================================
- Hits         3573     3570       -3     
- Misses        656      660       +4     
  Partials       28       28              

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