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

[KaranChadha10]

Description

This pull request contains the following changes

• Converted block-scoped namespaces to file-scoped namespaces for consistency in Data Structures 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

❌ Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.20%. Comparing base (ca458ab) to head (cb20589).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...es/LinkedList/SinglyLinkedList/SinglyLinkedList.cs	50.00%	0 Missing and 2 partials ⚠️
DataStructures/Tries/Trie.cs	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #525   +/-   ##
=======================================
  Coverage   95.20%   95.20%           
=======================================
  Files         272      272           
  Lines       10875    10875           
  Branches     1529     1529           
=======================================
  Hits        10353    10353           
  Misses        397      397           
  Partials      125      125           

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[Copilot]

Pull Request Overview

This PR modernizes C# data structure files by introducing a GlobalUsings.cs file with project-wide using directives and cleaning up redundant namespace imports. The changes align with C# 10+ style guidelines and improve code consistency.

• Added a global usings file with commonly used System namespaces
• Removed redundant using statements from individual files that are now globally available
• Converted from block-scoped to file-scoped namespaces where applicable

Reviewed Changes

Copilot reviewed 43 out of 43 changed files in this pull request and generated 1 comment.

File	Description
DataStructures/GlobalUsings.cs	Introduces global using directives for System, System.Collections.Generic, System.Linq, and System.Text
Various data structure files	Removes redundant using statements now covered by global usings
DataStructures/LinkedList/CircularLinkedList/CircularLinkedList.cs	Maintains block-scoped namespace (inconsistent with other files)

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[siriak]

Looks good, thanks!