Add test for `echo_range` for EK80 reduced sampling rate data

[leewujung]

This is a leftover from #968 where the echo_range output dimension should also be checked for EK80 reduced sampling rate data.

More elaboration: Here the reduced sampling rate refers to a specific setup the EK80 instrument allows. That setup would make the discretization along the range_sample axis coarser in the EchoData object (from the open_raw function), which affects the echo_range values in the output of compute_Sv. The intention of #969 is to check the calculation against the expected values from another program.

I got some sample data from a colleague from #702, and will put that somewhere for you to download, and the expected values it should be tested against.

[MohamedNasser8]

Hello @leewujung here I should make test on the echo_range to make sure it's dimension is equal to the

num_of_channels*length_of_bing_time*length_of_sample_range