Add Optional Timestamps Support to Models

[armanist]

This PR adds opt-in automatic timestamps for DbModel via the new HasTimestamps trait.
Models using the trait automatically manage created_at (on insert) and updated_at (on insert/update), with support for custom column names and unix/datetime formats.
Manual timestamp assignments were removed from demo services/controllers where redundant, and unit tests were added to cover default + custom behavior.

[codecov]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.46%. Comparing base (3c5fbce) to head (e60f11c).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Model/Traits/SoftDeletes.php	88.88%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #411      +/-   ##
============================================
+ Coverage     80.84%   81.46%   +0.62%     
- Complexity     2669     2685      +16     
============================================
  Files           238      239       +1     
  Lines          7114     7147      +33     
============================================
+ Hits           5751     5822      +71     
+ Misses         1363     1325      -38     

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[charoyan88]

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