Add support for additional RoundingMode enums (TowardsZero, AwayFromZero, NegativeInfinity)

[nanasess]

Summary

Currently, the bcmath polyfill only supports 4 of the 7 RoundingMode enum values introduced in PHP 8.4:

Currently Supported:

• RoundingMode::HalfAwayFromZero (maps to PHP_ROUND_HALF_UP)
• RoundingMode::HalfTowardsZero (maps to PHP_ROUND_HALF_DOWN)
• RoundingMode::HalfEven (maps to PHP_ROUND_HALF_EVEN)
• RoundingMode::HalfOdd (maps to PHP_ROUND_HALF_ODD)

Not Yet Supported:

• RoundingMode::TowardsZero
• RoundingMode::AwayFromZero
• RoundingMode::NegativeInfinity

These three modes currently throw a ValueError with the message "RoundingMode::{mode} is not supported" when used with BCMath::round().

Proposed Implementation

Add support for the remaining three rounding modes in the BCMath::round() method:

1. TowardsZero: Always round towards zero (truncate)

   • Positive numbers: round down (floor)
   • Negative numbers: round up (ceil)

2. AwayFromZero: Always round away from zero

   • Positive numbers: round up (ceil)
   • Negative numbers: round down (floor)

3. NegativeInfinity: Always round towards negative infinity (floor)

   • Both positive and negative numbers use floor behavior

Benefits

• Complete compatibility with PHP 8.4's native RoundingMode enum
• Consistent behavior across all PHP versions (8.1-8.4+)
• Better developer experience when migrating to/from native bcmath extension

Implementation Notes

The implementation should:

• Update BCMath::convertRoundingMode() to handle the new modes
• Update BCMath::bcroundHelper() or create specialized logic for these modes
• Add comprehensive test coverage for all rounding scenarios
• Maintain backward compatibility with existing functionality

Acceptance Criteria

• RoundingMode::TowardsZero works correctly for positive and negative numbers
• RoundingMode::AwayFromZero works correctly for positive and negative numbers
• RoundingMode::NegativeInfinity works correctly for positive and negative numbers
• All edge cases are handled (zero, very small numbers, large numbers)
• Test coverage includes precision scenarios and boundary conditions
• Documentation is updated to reflect the new supported modes