refactor: migrate to file-scoped namespaces and remove unused global usings statements

[KaranChadha10]

Summary of the change

This pull request contains the following changes

• Converted block-scoped namespaces to file-scoped namespaces for consistency
• 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 modernizes the C# codebase by migrating from block-scoped to file-scoped namespaces and removing unused global using statements to align with C# 10+ conventions and improve code clarity.

• Converts all block-scoped namespaces (namespace X { }) to file-scoped namespaces (namespace X;)
• Removes unused global using directives across multiple files
• Updates code formatting to follow modern C# style guidelines

Reviewed Changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
DataStructures/Hashing/NumberTheory/PrimeNumber.cs	Removed unused System imports and migrated to file-scoped namespace
DataStructures/Hashing/Entry.cs	Removed unused System and local imports, migrated to file-scoped namespace
DataStructures/DisjointSet/DisjointSet.cs	Removed unused System.Collections import, migrated to file-scoped namespace
DataStructures/Cache/LruCache.cs	Removed unused System import
DataStructures/Cache/LfuCache.cs	Removed unused System import
Algorithms/Stack/ReverseStack.cs	Converted to file-scoped namespace
Algorithms/Stack/NextGreaterElement.cs	Converted to file-scoped namespace
Algorithms/Stack/BalancedParenthesesChecker.cs	Converted to file-scoped namespace
Algorithms/Sorters/Utils/GallopingStrategy.cs	Removed unused imports and converted to file-scoped namespace
Algorithms/Sorters/Comparison/BasicTimSorter.cs	Removed unused System.Collections import and converted to file-scoped namespace
Algorithms/Shufflers/RecursiveShuffler.cs	Converted to file-scoped namespace
Algorithms/Shufflers/NaiveShuffler.cs	Converted to file-scoped namespace
Algorithms/Shufflers/LINQShuffler.cs	Removed unused imports and converted to file-scoped namespace
Algorithms/RecommenderSystem/ISimilarityCalculator.cs	Removed unused System imports
Algorithms/Other/Triangulator.cs	Removed unused imports and converted to file-scoped namespace
Algorithms/Other/JulianEaster.cs	Removed unused System.Globalization import
Algorithms/Other/Geohash.cs	Removed unused imports and converted to file-scoped namespace
Algorithms/Other/Geofence.cs	Removed unused imports and converted to file-scoped namespace
Algorithms/Numeric/KrishnamurthyNumberChecker.cs	Removed unused System import
Algorithms/Numeric/AdditionWithoutArithmetic.cs	Removed unused System and System.Numerics imports

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[codecov]

Codecov Report

❌ Patch coverage is 99.18033% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.14%. Comparing base (00e9bc4) to head (f7d23cb).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
Algorithms/Sorters/Comparison/BasicTimSorter.cs	97.72%	0 Missing and 1 partial ⚠️
Algorithms/Stack/BalancedParenthesesChecker.cs	96.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #521      +/-   ##
==========================================
- Coverage   95.19%   95.14%   -0.05%     
==========================================
  Files         272      272              
  Lines       10921    10921              
  Branches     1536     1536              
==========================================
- Hits        10396    10391       -5     
- Misses        400      403       +3     
- Partials      125      127       +2     

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[siriak]

Looks good, thanks!