Project DataStructures.Tests - Switch to file-scoped namespaces

[gmottajr]

Project DataStructures.Tests

Switch to file-scoped namespaces
Issue 425 - Migrate to DotNet 8

Motivation and Context
Github issue #425: Proposed to update to File-scoped namespaces. It was requested to perform the changes in a few PRs to make them smaller and easier to review. This is the one only meant to Switch to file-scoped namespaces of the project DataStructures.Tests.

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e8ca3f4) 94.50% compared to head (2e20e1b) 94.41%.

Additional details and impacted files

@@ Coverage Diff @@ ## master #436 +/- ## ========================================== - Coverage 94.50% 94.41% -0.10%  ========================================== Files 234 234 Lines 9843 9843 Branches 1455 1455 ========================================== - Hits 9302 9293 -9  - Misses 381 387 +6  - Partials 160 163 +3 

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[siriak]

Looks good, thanks!