Update Armstrong.java

[Patient-Pace-Coder]

Optimized Armstrong number check by removing string conversion

• 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

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 73.75%. Comparing base (bd785de) to head (2b9869b).

Files with missing lines	Patch %	Lines
...c/main/java/com/thealgorithms/maths/Armstrong.java	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6131      +/-   ##
============================================
- Coverage     73.77%   73.75%   -0.02%     
- Complexity     5120     5121       +1     
============================================
  Files           658      658              
  Lines         17619    17620       +1     
  Branches       3391     3391              
============================================
- Hits          12998    12996       -2     
- Misses         4117     4119       +2     
- Partials        504      505       +1     

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

[siriak]

Looks good, thanks!