Count UTF-8 characters by counting non-continuation bytes.
A continuation byte has the bit pattern 10xxxxxx (0x80..0xBF).
Every other byte starts a new character (ASCII, multi-byte leader, or invalid).
Count lines and words using optimized strategies per locale.
UTF-8: fused single-pass for lines+words to avoid extra data traversal.
C locale: single scalar pass with 3-state logic and ASCII run skipping.
Count lines + words + bytes in a single fused pass (the default wc mode).
Avoids separate passes entirely — combines newline counting with word detection.
Parallel counting of lines + words + bytes only (no chars).
Optimized for the default wc mode: avoids unnecessary char-counting pass.
C locale: single fused pass per chunk counts BOTH lines and words.
UTF-8 with pure ASCII data: falls back to parallel C locale path.