98 create x yz decomposer for quantify scheduler

[juanboschero]

This was originally supposed to be an ZXY decompose but it was shown that a XYX is more efficient and is native to quantify scheduler gates.

Changes include:

• Add XYX decomposer in decomposer folders
• Add tests for XYX

[rturrado]

Going back to the original issue:

Quantify-scheduler's gate library supports RZ and RXY. This last gate can represent any bloch sphere rotation of any angle provided the axis is in the plan (X, Y).

Currently we use the ZYZ decomposition to decompose gates for quantify-scheduler. This requires 3 gates.

But since QS supports RXY, it is possible that in a lot (all?) cases, only 2 of those gates are required to describe an arbitrary single-qubit unitary.

Goal of this issue:

investigate if there exists a mathematical unitary decomposition for 2x2 unitaries into either RZ.RXY or RXY.RZ implement corresponding decomposer and use it for quantify-scheduler

• I don't think QuantifyScheduler needs an XYX decomposition. They already have ZYZ.
• BTW, isn't an XYX basically an X90 plus a ZYZ?
• I would still insist on addressing the first point there: investigate if there exists a mathematical unitary decomposition for 2x2 unitaries into either RZ.RXY or RXY.RZ.