Make the time_0 in decay framework required and an astropy quantity

[wkerzendorf]

Currently the IsotopeAbundance dataframe subclass does not require a time_0 but will just assume 0 days and move on.
This should be clearly specified and not just an assumption. We need to raise an error if this is not specified and tell the users to specify this in the config or elsewhere.

[Soumya624]

Hi @wkerzendorf ,

I have worked on this. As I was going through the "\tardis\io\decay.py" file, I feel if I change the current init method in line 11, then it can be resolved.

Here is a modified version of the init method that includes a check to ensure that the time_0 parameter is specified by the user:

This modified version first checks if the time_0 parameter is included in the kwargs dictionary. If it is not, it raises a ValueError to inform the user that the time_0 parameter must be specified. If the time_0 parameter is present, it is extracted from the kwargs dictionary and assigned to the time_0 variable. The time_0 key is then removed from the kwargs dictionary before calling the parent class's init method. Finally, the value of time_0 is assigned to the time_0 attribute of the IsotopeAbundance instance.

Result:

Please let me know if this approach is alright. I have updated the PR in #2183