Fix: NumberFormatException with non-ASCII Unicode digits in MyAtoi

[vizahat36]

Fixes #7205 (reported by @lionel-w2).

This PR resolves an issue in where non-ASCII Unicode digit characters (e.g., Arabic-Indic digit ١) were incorrectly accepted by Character.isDigit() but parsed using ASCII arithmetic, leading to invalid parsing behavior.

The digit validation logic has been updated to accept only ASCII digits ('0'–'9'), ensuring correct and predictable atoi behavior consistent with C/C++ semantics.

Changes

• Replaced Character.isDigit(ch) with an explicit ASCII digit range check
• Ensures unsupported Unicode digits are treated as non-digit characters
• Prevents incorrect numeric accumulation

Testing

• All existing tests pass
• Verified edge cases including Unicode digits, whitespace, signs, overflow, and empty input

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.09%. Comparing base (0f9139d) to head (e9d593a).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7231      +/-   ##
============================================
- Coverage     79.10%   79.09%   -0.01%     
- Complexity     6973     6974       +1     
============================================
  Files           783      783              
  Lines         22950    22950              
  Branches       4512     4512              
============================================
- Hits          18154    18152       -2     
- Misses         4076     4077       +1     
- Partials        720      721       +1     

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