Auto merge of #143730 - pascaldekloe:fmt-radix-trim, r=tgross35

fmt of non-decimal radix untangled

Have the implementation match its decimal counterpart.

* Digit table instead of conversion functions
* Correct buffer size per radix
* Elimination of dead code for negative
* No trait abstraction for integers

#### Original Performance
```
    fmt::write_10ints_bin                                                393.03ns/iter      +/- 1.41
    fmt::write_10ints_hex                                                316.84ns/iter      +/- 1.49
    fmt::write_10ints_oct                                                327.16ns/iter      +/- 0.46
```

#### Patched Performance
```
    fmt::write_10ints_bin                                                392.31ns/iter      +/- 3.05
    fmt::write_10ints_hex                                                302.41ns/iter      +/- 5.48
    fmt::write_10ints_oct                                                322.01ns/iter      +/- 3.82
```

r? tgross35

Author: bors