Replace `str::bytes().count()` with `str::len()`

Rust pattern

str::bytes().count() is longer and may not be as performant as using str::len().

Apply with the Grit CLI
grit apply byte_count_to_len

Replaces a simple str::bytes().count()

BEFORE 
let my_len = "hello".bytes().count();
AFTER 
let my_len = "hello".len();