Add comprehensive documentation for bytes_util package

[peter-jerry-ye]

Summary

This PR adds comprehensive documentation to the src/internal/bytes_util package to improve code maintainability and developer experience.

Changes Made

Documentation Improvements

• Added detailed doc comments to ascii_to_string function with:
  • Clear parameter descriptions
  • Return value documentation
  • Behavior explanation for different character types
  • Working code example using proper @encoding/utf8.encode

New Files

• README.mbt.md: Complete package documentation including:

  • Package overview and purpose
  • Function descriptions with usage notes
  • Integration context within the async library

• util_test.mbt: Comprehensive test suite covering:

  • Printable ASCII characters
  • Control characters (newline, tab, carriage return)
  • Edge cases and proper escaping behavior

Code Quality

• All tests pass successfully (moon test)
• Code compiles without errors (moon check)
• Documentation follows MoonBit standards with proper formatting
• Uses current encoding practices (@encoding/utf8.encode instead of deprecated to_bytes())

Testing

All existing functionality is preserved and new tests validate:

• Correct handling of printable ASCII (32-126)
• Proper escaping of control characters
• Hexadecimal representation of non-printable bytes
• Function behavior matches documentation

The package is used internally by the TLS module for error message formatting, and this documentation will help future maintainers understand its purpose and usage patterns.

[coveralls]

Pull Request Test Coverage Report for Build 645

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 79.037%

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Totals
Change from base Build 641:	0.07%
Covered Lines:	1165
Relevant Lines:	1474

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💛 - Coveralls