Implement benchmarks

We need to provide benchmarks to compare performance with existing popular solutions:
https://github.com/dbalabka/php-enumeration#existing-solutions
[PHPBench](https://github.com/phpbench/phpbench) is a great tool for this.

Start by reviewing the existing-solutions comparison linked in the issue and the PHPBench tool documentation. Define the benchmark scope from the listed popular solutions, then add benchmarks that make their performance comparable. Done means the repository provides runnable benchmark results for the intended comparisons.

Written by the indexing model from the issue text.