chore: add GlobalUsings.cs with project-wide using directives in utilities and utilities tests folder

[KaranChadha10]

Description

This pull request contains the following changes

• Converted block-scoped namespaces to file-scoped namespaces for consistency in Utilitites and Utilities.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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.19%. Comparing base (767c45a) to head (0fc1039).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #523   +/-   ##
=======================================
  Coverage   95.18%   95.19%           
=======================================
  Files         272      272           
  Lines       10921    10921           
  Branches     1536     1536           
=======================================
+ Hits        10395    10396    +1     
  Misses        400      400           
+ Partials      126      125    -1     

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[Copilot]

Pull Request Overview

This PR introduces global using directives to reduce boilerplate code across the Utilities and Utilities.Tests projects. The changes include adding GlobalUsings.cs files to centralize commonly used namespace imports and removing redundant using statements from individual files.

• Added GlobalUsings.cs files to both Utilities and Utilities.Tests projects with core .NET namespaces
• Removed redundant using statements from extension classes and test files
• Maintained file-scoped namespace declarations for consistency with modern C# conventions

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Utilities/GlobalUsings.cs	Defines global using directives for System, System.Collections.Generic, and System.Linq
Utilities.Tests/GlobalUsings.cs	Defines global using directives including test-specific namespaces (FluentAssertions, NUnit.Framework)
Utilities/Extensions/*.cs	Removed redundant using statements now covered by global usings
Utilities/Exceptions/ItemNotFoundException.cs	Removed redundant System using statement
Utilities.Tests/Extensions/*.cs	Removed redundant using statements now covered by global usings

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[siriak]

Looks good, thanks!