linalg bug fix & cython integration

[ryanhill1]

Summary of changes

• Fixed small bug in so_bidiagonalize
• Migrated kronecker_fator function to Cython (~60% speedup)
• Migrated so4_to_so2 function to Cython (~5% speedup)
• These initial Cython migrations weren't as much out of concern for performance, but rather done as more of an experiment and to learn how it works. Now that the structure is there, we may be able to migrate some of the other larger functions and get an actual performance improvement out of kak_decomposition_angles, if we wanted to.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

📢 Thoughts on this report? Let us know!

[TheGupta2012]

I like the idea here and the speed up is pretty good! Going forward, do you think it would be better to arrange the .pyx files in a cython folder and rename the .pyx file as the module name? Eg. -

1. src/pyqasm/linalg_cy.pyx becomes src/pyqasm/cython/linalg.pyx and
2. from pyqasm.linalg_cy becomes from pyqasm.cython.linalg import ...

[TheGupta2012]

Looks good! Thanks for the changes