Add 7-day cooldown for NuGet Dependabot updates

[Copilot]

Dependabot currently opens NuGet update PRs on its weekly schedule without a delay window. This change adds a 7-day cooldown so NuGet update PRs are deferred before being raised.

• Dependabot policy update
  • Added cooldown configuration to the NuGet update entry in .github/dependabot.yml.
  • Set default-days to 7 to apply a one-week cooldown to NuGet version updates.

updates:
  - package-ecosystem: "nuget"
    directory: "/"
    schedule:
      interval: "weekly"
    cooldown:
      default-days: 7

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.22%. Comparing base (3c441e7) to head (8f72d1e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #357   +/-   ##
=======================================
  Coverage   96.22%   96.22%           
=======================================
  Files          56       56           
  Lines        7707     7707           
  Branches      897      897           
=======================================
  Hits         7416     7416           
  Misses        176      176           
  Partials      115      115           

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