Clarify setting of Project::unavailable_samples_count attribute

[avrohomgottlieb]

Context

The unavailable_samples_count attribute represents all samples that do not have data files associated with them, but are included a project's sample_metadata.csv file. We update the Project::unavailable_samples_count in Project::update_downloadable_sample_count, which is called in loader::generate_computed_files after the completion of computed file generation.

Problem or idea

The way that we currently couple the setting of unavailable_samples_count alongside downloadable_sample_count is not necessarily the optimal approach, as we already know whether or not a sample is unavailable when its loaded into the database and don't need to wait until after computed file generation. Instead, we should set it in Project::update_project_aggregate_properties with other aggregate attributes.

Solution or next step

class Project(...):
    ...

    def update_project_aggregate_properites(self):
        ...
        self.unavailable_samples_count = self.samples.filter(
            has_single_cell_data=False, has_spatial_data=False
        ).count()
        self.save()