There is no way to align progress bars in MultiBar

Here is what I see:

```
7.85 GB / 13.96 GB ╢██████████████████████████░░░░░░░░░░░░░░░░░░░░░░░░░░░╟ 56.26 % 1.41 GB/s 4s
7.82 GB / 7.82 GB ╢██████████████████████████████████████████████████████╟ 100.00 % 39.08 GB/s
3.37 GB / 21.79 GB ╢██████████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░╟ 15.49 % 664.74 MB/s 28s
```

Instead, it would be nice to see something like following:

```
7.85 GB / 13.96 GB ╢██████████████████████████░░░░░░░░░░░░░░░░░░░░░░░░╟ 56.26 % 1.41 GB/s 4s
7.82 GB / 7.82 GB ╢██████████████████████████████████████████████████╟ 100.00 % 39.08 GB/s
3.37 GB / 21.79 GB ╢██████████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░╟ 15.49 % 664.74 MB/s 28s
```

Look at the MultiBar implementation in the source code, likely in src/multibar.rs or similar. Understand how the progress bars are currently formatted and printed. The goal is to align the numbers (like '13.96 GB' and '7.82 GB') by padding them to a fixed width, and similarly align the percentages and speed units. Check existing tests for formatting to see how to add this feature without breaking existing behavior.

索引モデルが issue の本文から書いたものです。