Docs and Tests for Format

[ardasener]

This pr will add a test suite and documentation comments for the members of sparsebase::format namespace. The test suites includes 3 different types of tests for each concrete class derived from sparsebase::format::Format:

1. Basics: Stores some data on the format instance and checks the integrity and the dimensions of the data.
2. Ownership: Creates two format instances using the same data with only one them set to owned. Then attempts to delete both instances. In a successful run, only the owned instance will deallocate the memory hence no runtime errors will be encountered. Note that I found no way to verify if the memory is actually deallocated properly, as a result I suggest adding a "memory leak check" step to our Github Actions configuration (which can use an external program like valgrind).
3. Release: Creates a format instance set to owned. Then releases the data using the release_xxx() member functions. Then both the data and the format instance is deleted. Since the data is released from the instance a double delete should not occur in a successful run.