implement tensors in binsparse

[junikimm717]

• a separate bsp_tensor_t field is returned.

[willow-ahrens]

@BenBrock Here's the PR to add tensors to the spec, please review when you get the chance!

[BenBrock]

@junikimm717 @willow-ahrens Thanks for submitting the PR! At first glance everything looks generally good. I see two small problems:

1. Missing SPDX headers on some of the new files (see example here)
2. Incorrect path in testing infrastructure (see CI error here.).

I would also prefer to add a new flag ENABLE_TENSOR_TESTS or something like that to enable/disable the new tests (since they require Julia as an external dependency).

I'm also happy to fix these issues myself, but I have a busy week with a deadline coming up, so I probably won't be able to spend time on this until next week.

[willow-ahrens]

Currently, the tensor tests only run if Julia is installed. Is this sufficient?

[BenBrock]

Yes, requiring Julia for the tensor tests is fine for now, as long as we can run the CI in GitHub actions. (That should be no problem.)