Aho-Corasick multi-pattern string matching

Multi-pattern matching over byte strings in pure OCaml, with no runtime dependencies beyond the standard library. Supports overlapping search, lazy iteration, leftmost-longest selection, replacement, ASCII case folding, and chunked streaming in three match modes. Automata are immutable and reusable. Search is linear in the input plus matches examined; leftmost-longest selection uses lookahead bounded by the longest pattern.