--keep-right not keeping right on long lines with search term present

### Checklist

- [x] I have read through the manual page (`man fzf`)
- [x] I have searched through the existing issues
- [x] For bug reports, I have checked if the bug is reproducible in the latest version of fzf

### Output of `fzf --version`

0.66.1 (brew)

### OS

- [ ] Linux
- [x] macOS
- [ ] Windows
- [ ] Etc.

### Shell

- [ ] bash
- [x] zsh
- [ ] fish

### Problem / Steps to reproduce

When long lines are present the `--keep-right` option seems to lose effect as soon as a search term is entered and results are being highlighted.

Here's an example:

```bash
(cat < this ╰──────────────────────────────────────╯
```

As you can see the search term `this` has moved to the middle of the line, violating the `--keep-right` option, even though there would be enough room to show the entire rightmost part of the line while still keeping `this` in view.

(Of course ignoring keep-right is fine when the search term occurs so far on the left that it's not possible to keep the right edge in view.)

Reproduce the supplied fzf command in an 80x15 terminal, then start at the --keep-right option handling and the rendering path where highlighted matches affect horizontal positioning. Done means the rightmost portion remains visible when the search term is highlighted whenever there is enough room, with regression coverage for this example.

Written by the indexing model from the issue text.