fix: correct package declaration for NearestElement and update test imports

[sgindeed]

• 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

❌ Patch coverage is 85.71429% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.82%. Comparing base (3eb521b) to head (b4739f8).

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/stacks/NearestElement.java	85.71%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6688      +/-   ##
============================================
+ Coverage     75.80%   75.82%   +0.02%     
- Complexity     5804     5824      +20     
============================================
  Files           705      706       +1     
  Lines         19846    19888      +42     
  Branches       3851     3863      +12     
============================================
+ Hits          15045    15081      +36     
- Misses         4218     4224       +6     
  Partials        583      583              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.