…ges"

This reverts commit 16ce3cf, reversing
changes made to 3329a84.

Cattrs works by passing the value it is structuring into the default
constructor of the target type, so it supports Python's coercions.

In this case, consider the previous version of TextData:

class TextData:
  data: str
  type: "text" | "file"

When a test suite containing {'type': 'text', 'data': 500} is
structured, cattrs will attempt to structute `data` by doing `str(500)`.
This is legal, so cattrs happily accepts it.

The new definition, however, is as follows:

class TextData:
  content: ContentPath | str
  path: str | None = None

When the decorator runs and returns the value from data as an int,
cattrs will take over, trying to structure it into `ContentPath | str`.
TESTed has a custom union structuring function to allow structuring
into any union. One thing it does not do, however, is the data coercion.

The union structuring requires exact types, which is why the code failed
and the old test suite no longer works.

To fix this, we now explicitly coerce the legacy data to a string inside
the fallback converter before it reaches the strict union hook.

Another attempt for `stdin`

Support `input_files`

Add support for `output_files`