[PROPOSAL] Let MIMO launch the pseudonymize process

## Actual usage

```console
$ mkfifo real.jsonl
$ lino pull bdd | tee real.jsonl | pimo | mimo real.jsonl | lino push bdd
```

## Wanted usage

```console
$ # mimo starts the subprocess (pimo)
$ lino pull bdd | mimo pimo | lino push bdd
```

or

```console
$ # mimo reads masked data from a file
$ lino pull bdd | tee real.jsonl | pimo | mimo --from-file real.jsonl | lino push bdd
```

Start at the mimo CLI entry point and trace how it currently consumes the masked-data file in the shown pipeline. Compare that behavior with the two wanted command forms, then verify that subprocess launching and file-based input both work with the example pipelines.

Written by the indexing model from the issue text.