TdtIO is not loading sev data for new-style datasets

[JuliaSprenger]

Describe the bug
For recent datasets the continuous data stored in the sev files are not accompanied by timestamp data in the tsq file. As the tsq file is used to determine the number of samples of a signal, this leads to no signal to be loaded from new-style sev files.

To Reproduce
Add a new test to the test_tdtrawio.py

    def test_sev_data_is_loaded(self):
        filename = self.get_local_path('tdt/dataset_0_single_block/'
                                       '512ch_reconly_all-181123_B24_rest.Tdx')
        io = TdtRawIO(filename)
        io.parse_header()
        # check that all signals contain data
        for stream_index in range(len(io.header['signal_channels'])):
            size = io.get_signal_size(block_index=0, seg_index=0, stream_index=stream_index)
            self.assertNotEqual(size, 0)

Expected behaviour
Signals from sev files should not be empty.

[ree-gupta]

Related issue on the spikeinterface repository here

Also #1129

[mberns-ru]

Hi! @zm711 linked my thread and asked if I could provide some sample files. Here is a folder of 1-minute recordings in the format my lab has been using (64 .sev files, 1 per channel).