Improve tr performances (Closes: #8439)

[sylvestre]

Results:

$ dd if=/dev/zero bs=1M count=10 | tr '\0' 'x' > 10mb_input
$ hyperfine --export-markdown tr.md --warmup 3 \
    '/usr/bin/tr a b < 10mb_input > /dev/null' \
    './target/release/tr a b < 10mb_input > /dev/null' \
    './target/release/tr.previous a b < 10mb_input > /dev/null'
Benchmark 1: /usr/bin/tr a b < 10mb_input > /dev/null
  Time (mean ± σ):       6.5 ms ±   0.7 ms    [User: 4.1 ms, System: 2.4 ms]
  Range (min … max):     5.1 ms …  10.3 ms    520 runs

Benchmark 2: ./target/release/tr a b < 10mb_input > /dev/null
  Time (mean ± σ):      10.7 ms ±   0.8 ms    [User: 7.9 ms, System: 2.7 ms]
  Range (min … max):     9.7 ms …  15.3 ms    271 runs

Benchmark 3: ./target/release/tr.previous a b < 10mb_input > /dev/null
  Time (mean ± σ):      61.2 ms ±   2.2 ms    [User: 58.5 ms, System: 2.5 ms]
  Range (min … max):    58.4 ms …  66.9 ms    47 runs

Summary
  /usr/bin/tr a b < 10mb_input > /dev/null ran
    1.64 ± 0.23 times faster than ./target/release/tr a b < 10mb_input > /dev/null
    9.39 ± 1.12 times faster than ./target/release/tr.previous a b < 10mb_input > /dev/null

Not as fast as GNU but much better than the previous implementation

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
/usr/bin/tr a b < 10mb_input > /dev/null	6.5 ± 0.7	5.1	10.3	1.00
./target/release/tr a b < 10mb_input > /dev/null	10.7 ± 0.8	9.7	15.3	1.64 ± 0.23
./target/release/tr.previous a b < 10mb_input > /dev/null	61.2 ± 2.2	58.4	66.9	9.39 ± 1.12

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)

[drinkcat]

The u8 array scared me at first, but... this is broken anyway ,-)

echo "Héállo" | env tr -d 'é' | hexdump -C
00000000  48 a1 6c 6c 6f 0a                                 |H.llo.|

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/stdbuf (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)

[drinkcat]

6x improvement is great start! ,-P Thanks!