optimize EscapeAscii's Display and CStr's Debug
```
old:
ascii::bench_ascii_escape_display_mixed 17.97µs/iter +/- 204.00ns
ascii::bench_ascii_escape_display_no_escape 545.00ns/iter +/- 6.00ns
new:
ascii::bench_ascii_escape_display_mixed 4.99µs/iter +/- 56.00ns
ascii::bench_ascii_escape_display_no_escape 91.00ns/iter +/- 1.00ns
```
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| .. | ||
| benches | ||
| src | ||
| tests | ||
| Cargo.toml | ||