Adds a divan-based benchmark suite under src/uu/tr/benches/ that
codspeed can build and run, and registers uu_tr in the benchmarks
workflow matrix. Each bench redirects fd 0 to a prepared file and
fd 1 to /dev/null around uumain since tr only reads stdin.
Covers the AVX2 ASCII-range fast path, single-char replace,
multi-char table translation, and ASCII range delete, at 1/16/64 MB.
jeffhuang
2fcd54344d