Fix date time handling in chapter 1

[meaboutsoftware]

This PR includes changes related to switching custom system clock abstraction (built on .NET 7) with TimeProvider (built-in .NET 8)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 96.49%. Comparing base (7695cc7) to head (501c0a7).
Report is 16 commits behind head on main.

Files	Patch %	Lines
...ntracts/SignContract/Events/ContractSignedEvent.cs	75.00%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #108      +/-   ##
==========================================
- Coverage   96.81%   96.49%   -0.32%     
==========================================
  Files          61       61              
  Lines         533      542       +9     
  Branches        9        9              
==========================================
+ Hits          516      523       +7     
- Misses         14       16       +2     
  Partials        3        3              

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