Add bell-flagged circuits

[oscarhiggott]

This PR adds bell-flagged ("standard color code") circuits (from [Bair+19]) into the clorco directory of chromobius.

This is the diagram of the circuit from Figure 2 of the chromobius paper:

For example, with this PR, to generate a bell-flagged circuit you could use:

from clorco._make_circuit import make_circuit

circuit = make_circuit(
    style=f"bell_flagged_color_code_X",
    noise_model=gen.NoiseModel.si1000(0.001),
    noise_strength=0.001,
    rounds=5,
    diameter=5,
    convert_to_cz=True,
    editable_extras={}
)

Within each cycle, and for each plaquette (red, green or blue), there is an "X stabilizer" detector, the "X stabilizer flag" detector that it's paired with (measured at the same time step), as well as the "Z stabilizer" detector and the "Z stabilizer flag" detector it's paired with. The fourth coordinate of the "X stabilizer" and "Z stabilizer" detectors have the same convention as the other color code circuits in this repository:

0 = Red X
1 = Green X
2 = Blue X
3 = Red Z
4 = Green Z
5 = Blue Z

The fourth coordinate of the detector for a flag detector has the value c+6 where c is the fourth coordinate of the detector it is "paired" with. i.e.:

6 = Red X flag
7 = Green X flag
8 = Blue X flag
9 = Red Z flag
10 = Green Z flag
11 = Blue Z flag

Note that the "Red X flag" detector is a Z measurement that flags potential hook errors in the "Red X" stabilizer measurement sub-circuit. Note also that the coordinates of the flags are not compatible with the chromobius decoder (which accepts coordinates in {-1, 0, 1, 2, 3, 4, 5}) but might be useful for other decoders.