New gate organisation

[mateuszkupper]

Reorganisation of all optyx generators into two categories: user-facing and back-end. User-facing generators are subclasses of Channel - they represent physical gates or operations which are of use in building hybrid photon-qubit circuit. The back-end classes (core) are the graphical languages on which the user-facing channels are based on - they provide a way to define Kraus maps for the user-facing channels.

Qubit primitives:

Category	Primitives	Description
Circuits	Circuit, QubitChannel	Quantum circuits and channels operating on qubits.
ZX	Z, X, H, Scalar, Bra, Ket	Core ZX-calculus generators (spiders, Hadamard, scalar).
Errors	BitFlipError, DephasingError	Stochastic error channels acting on qubits.
Classical-quantum	Encode, Discard, Measure	Channels for encoding, discarding, and measuring qubits.

Photonic primitives:

Category	Primitives	Description
Measurements	Discard, PhotonThresholdMeasurement, NumberResolvingMeasurement	Operations that discard modes or measure photon number (threshold or resolving).
Linear optical gates	Gate, Phase, BBS, TBS, MZI, ansatz	Unitary transformations built from beam splitters, phase shifters, and general interferometers.
Dual-rail operators	DualRail, HadamardBS, PhaseShiftDR, ZMeasurementDR, XMeasurementDR, FusionTypeI, FusionTypeII	Gates and measurements for qubits encoded in dual-rail photonic modes.
States	Encode, Create	Preparation of photonic states and encoding of modes.
Other	NumOp, Scalar, PhotonLoss	Miscellaneous operators.

Classical primitives:

Category	Primitives	Description
Logic gates	NotBit, XorBit, AndBit, OrBit, CopyBit, SwapBit, Z, X, H	Boolean operations and ZX spiders acting on classical bits.
Arithmetic on modes	AddN, SubN, MultiplyN, DivideN, Mod2, CopyN, SwapN	Integer arithmetic and data-movement primitives on natural-number modes.
Control & routing	BitControlledGate, BitControlledPhaseShift, ClassicalFunction, BinaryMatrix	Classical control of quantum gates and generic functions/matrix maps on bit or mode registers.
Bit, digits & selection	PostselectBit, PostselectDigit, DiscardBit, DiscardMode, Select, Digit, Bit, Id, Scalar	State preparation, post-selection, discarding, and identity/scalar boxes for classical data.

Note: the functionality to convert to optyx from tket is not available until the tket->discopy conversion method (no init_and_discard) is modified.

[giodefelice]

Looks very good! A couple of things:

1. There is an error message in the ZX transpilation notebook. That notebook can be removed all-together.

2. The LO diagrams obtained from dual_rail_encoding map are huge and clutter the documentation. Remove this from everywhere except maybe in the zx module.

[giodefelice]

The comments can be handled in future PRs