feat: add soft delete mixin

[Kumzy]

Creating a mixin for soft delete.

Do you think we need more in the Mixin?

Missing tests + repository changes + documentation

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.50%. Comparing base (05a413b) to head (a2b3600).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
advanced_alchemy/mixins/softdelete.py	0.00%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #337      +/-   ##
==========================================
+ Coverage   79.26%   79.50%   +0.24%     
==========================================
  Files          87       88       +1     
  Lines        6355     6406      +51     
  Branches      810      824      +14     
==========================================
+ Hits         5037     5093      +56     
+ Misses       1068     1057      -11     
- Partials      250      256       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.