FCs not detected for processing

[kkappler]

Since the KernelDataset moved to mtpy, FCs are not being used for processing when present.

• Note that the fc column also defaults to False ... it should default to None, as we do not know if fcs are there until we have a processing config ... we may wish to remove it entirely in fact.
• In fact the presence of fcs, at least until now, was only relevant when fcs were used for processing. That column may want to go into processing summary.
  ...
  In any case, I am able to restore the desired behaviour by this PR in mtpy.

If that is no-go, then comment out the if statement around L168 in /aurora/pipelines/transfer_function_kernel.py

    def all_fcs_already_exist(self) -> bool:
        """Return true of all FCs needed to process data already exist in the mth5s"""
        if self.kernel_dataset.df["fc"].isna().any():
            self.check_if_fcs_already_exist()

        # these should all be booleans now
        assert not self.kernel_dataset.df["fc"].isna().any()

        return self.kernel_dataset.df.fc.all()