Project; DataStructure Switch to file-scoped namespaces

[gmottajr]

Issue 425 - File-scoped namespaces

Project; DataStructure
Switch to file-scoped namespaces

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 only for project DataStructure .

• 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

Attention: 148 lines in your changes are missing coverage. Please review.

Comparison is base (a354d01) 94.50% compared to head (e128e06) 94.50%.

Files	Patch %	Lines
...es/LinkedList/DoublyLinkedList/DoublyLinkedList.cs	69.59%	30 Missing and 15 partials ⚠️
DataStructures/Timeline.cs	87.50%	14 Missing and 3 partials ⚠️
DataStructures/RedBlackTree/RedBlackTree.cs	95.68%	10 Missing and 6 partials ⚠️
DataStructures/Heap/FibonacciHeap/FibonacciHeap.cs	91.92%	9 Missing and 4 partials ⚠️
DataStructures/AATree/AATree.cs	94.00%	5 Missing and 4 partials ⚠️
DataStructures/BitArray.cs	97.58%	5 Missing and 2 partials ⚠️
DataStructures/Stack/ListBasedStack.cs	73.91%	4 Missing and 2 partials ⚠️
DataStructures/Heap/PairingHeap/PairingHeap.cs	96.15%	1 Missing and 4 partials ⚠️
DataStructures/ScapegoatTree/ScapegoatTree.cs	97.17%	3 Missing and 2 partials ⚠️
DataStructures/Heap/MinMaxHeap.cs	97.59%	1 Missing and 3 partials ⚠️
... and 14 more

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #434   +/-   ##
=======================================
  Coverage   94.50%   94.50%           
=======================================
  Files         234      234           
  Lines        9843     9843           
  Branches     1455     1455           
=======================================
  Hits         9302     9302           
  Misses        381      381           
  Partials      160      160           

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[siriak]

Looks good, thanks!