fix: Guard against attribute errors in TesseractOcrModel __del__ (#1494)

This moves the initialization of the `reader` and `script_readers`
attributes to before we attempt to import tesserocr, so that when later
accessing these attributes in the garbage collection method `__del__`
the attributes exist.

This requires changing the typing of the `script_readers` dict value to
`Any` because we cannot yet reference its actual strong type, since it's
a tesserocr value.

This prevents throwing an exception during garbage collection for
cases where the TesseractOcrModel instance didn't properly initialize,
like when it throws an `ImportError` during its initializer.

Signed-off-by: Ben Browning <bbrownin@redhat.com>