Add C++23 ULID implementation (aurimasniekis/cpp-ulid)

[aurimasniekis]

This PR adds a C++ implementation of ULID to the README implementations list:

https://github.com/aurimasniekis/cpp-ulid

Details

• Header-only C++23 implementation
• Implements ULID per spec (128-bit identifier with 48-bit timestamp and 80-bit randomness)
• Supports generation, parsing (Base32, hex, bytes), and encoding
• Provides monotonic ULID generation within the same millisecond
• Lexicographically sortable with full comparison and hashing support
• Pluggable random number generator and clock for deterministic testing

Why include this

• Adds a modern, header-only C++ (C++23) implementation
• Covers advanced use cases such as monotonic generation and deterministic testing
• Integrates well with the C++ standard library (std::format, hashing, comparisons)