Add Rotation Synthesis subpackage

[NoureldinYosri]

The Rotation-Synthesis subpackage implements the state of the art rotation synthesis protocols for compiling $SU(2)$ unitaries into clifford+T gates. The current PR has the code for synthesis Z-rotations and I will send another PR for arbitrary axis rotations.

Please refer to qualtran/rotation_synthesis/README.md for usage examples.

[mpharrigan]

what's the deal with the requirements file? do you need to add mpmath?

[NoureldinYosri]

@mpharrigan I thought I did but Qualtran already depends on mpmath transitively through sympy

[mpharrigan]

can you go ahead and add it to runtime.txt since we import it directly. Don't bother with the pip-compile step if it won't change anything but the comments -- it will get picked up the next time that gets bumped

[NoureldinYosri]

@mpharrigan done

[mpharrigan]

reviewed offline