Implement sliding() and grouped() methods for Set collection

[magik092]

I needed functionality similar to PHP's array_chunk() but for immutable Set collections. This inspired me to implement sliding() and grouped() methods, bringing Munus closer to feature parity with Vavr (the Java functional library).

What's Changed

• ✅ Set::sliding(int $size, int $step): Set<Set> - Creates a sliding window over Set elements
• ✅ Set::grouped(int $size): Set<Set> - Groups elements into fixed-size chunks (delegates to sliding($size, $size))

Implementation Details

• Performance optimized: Uses array_slice() for efficient memory management with PHP's copy-on-write
• Immutability preserved: Returns new Set instances without modifying the original
• Comprehensive test coverage: 8 test cases covering various scenarios including:
  • Empty sets
  • Different window sizes and step values
  • Edge cases with remainder elements
  • Comparison between sliding() and grouped() behavior

API Examples

// Sliding window with overlap
$set = Set::of(1, 2, 3, 4, 5, 6, 7);
$result = $set->sliding(3, 1);
// Returns: Set(Set(1,2,3), Set(2,3,4), Set(3,4,5), Set(4,5,6), Set(5,6,7), Set(6,7), Set(7))
     
// Grouped chunks
$set = Set::of(1, 2, 3, 4, 5);
$result = $set->grouped(2);
// Returns: Set(Set(1,2), Set(3,4), Set(5))