chore: add GlobalUsings.cs with project-wide using directives in data structures tests

[KaranChadha10]

Description

This pull request contains the following changes

• Converted block-scoped namespaces to file-scoped namespaces for consistency in Data Structures Tests folder
• Removed redundant/unused global using directives to improve code clarity
• Aligned code formatting with project conventions and C# 10+ style guidelines

Issue link: #520

• 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

[Copilot]

Pull Request Overview

This pull request adds a GlobalUsings.cs file with project-wide using directives and removes redundant using statements from test files across the DataStructures.Tests project. This modernizes the codebase to use C# 10+ global using features for better code organization and reduces repetitive using declarations.

• Added GlobalUsings.cs with commonly used namespaces declared globally
• Removed redundant using statements from all test files that are now covered by global usings
• Minor code formatting improvement in one test method

Reviewed Changes

Copilot reviewed 43 out of 43 changed files in this pull request and generated 2 comments.

File	Description
DataStructures.Tests/GlobalUsings.cs	Introduces global using directives for common namespaces (System, NUnit.Framework, FluentAssertions, etc.)
Multiple test files	Removes redundant using statements now covered by global usings
DataStructures.Tests/Hashing/HashTableTests.cs	Minor formatting improvement to lambda expression

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[Copilot]

The NUnit.Framework.Internal namespace contains internal APIs that are not intended for public use and may change between versions. Consider removing this global using unless there's a specific need for internal NUnit functionality.

Suggested change

global using NUnit.Framework.Internal; // Internal NUnit infrastructure (test context, utilities) — generally used for advanced or framework-level test control

[siriak]

Please check the comments

[Copilot]

System.Collections contains legacy non-generic collection types that are generally discouraged in modern C# development. Consider removing this global using unless legacy collections are actively used throughout the test project.

Suggested change

global using System.Collections; // Non-generic collection types (e.g., ArrayList, Hashtable, IDictionary, ICollection)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.15%. Comparing base (f1fde96) to head (ba78eb4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #526      +/-   ##
==========================================
- Coverage   95.19%   95.15%   -0.04%     
==========================================
  Files         272      272              
  Lines       10920    10920              
  Branches     1536     1536              
==========================================
- Hits        10395    10391       -4     
- Misses        400      403       +3     
- Partials      125      126       +1     

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[siriak]

Re-request a review when the comments are addressed