ring_span lite

Single-file inclusion with no external dependencies beyond the C++ standard library, making integration simple and dependency-free, as stated in the README.

Supports C++98 through C++17 and later, enabling use in legacy codebases and across decades of C++ evolution, as highlighted in the features.

Follows the interface of proposed std::ring_span (P0059), ensuring future compatibility and a modern approach, with optional extensions for flexibility.

Configurable poppers (null_popper, default_popper, copy_popper) allow custom behavior on element removal, providing control over data management.

Optional power-of-two capacity optimization uses bitwise operations instead of modulo for efficiency, as noted in the synopsis.