docs: add time & space complexity for Stacks (#7132)"

[Srikar-Yekabote]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.90%. Comparing base (d9f2ac8) to head (2899f7e).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7165   +/-   ##
=========================================
  Coverage     78.90%   78.90%           
  Complexity     6853     6853           
=========================================
  Files           769      769           
  Lines         22668    22669    +1     
  Branches       4456     4456           
=========================================
+ Hits          17887    17888    +1     
  Misses         4067     4067           
  Partials        714      714           

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[DenizAltunkapan]

@Srikar-Yekabote please format your code with clang

[github-actions]

This pull request has been automatically closed because its workflows or checks failed and it has been inactive for more than 14 days. Please fix the workflows and reopen if you'd like to continue. Merging from main/master alone does not count as activity.