BUG: fix FRB integration with CylindricalResolutionBuffer

[neutrinoceros]

PR Summary

Fix #4789
This is a proof-of-concept level patch, I want to see how it performs against CI.
I'll need to write the missing bits in _set_radius and add an actual test.

This is currently based atop #4784

PR Checklist

• New features are documented, with docstrings and narrative docs
• Adds a test for any bugs fixed. Adds tests for new features.

[neutrinoceros]

I think I need to be reminded what "unitary" units mean

[neutrinoceros]

@yt-fido test this please

[forrestglines]

Thanks @neutrinoceros , very much appreciate the work on this.

The FRB's don't quite match what I'd expect. If I run the following code:

import yt
import numpy as np

import matplotlib as mpl
import matplotlib.pyplot as plt

ds = yt.load_sample("bw_polar_2d")

slc = yt.SlicePlot(ds, "z", ("gas", "density"))
frb = slc.data_source.to_frb(width=(4,"cm"),resolution=(512,512),center=(0,0))

minmax = lambda A : (np.nanmin(A).v[()],np.nanmax(A).v[()])

R = frb["r"].in_units("cm")
Theta = frb["theta"].in_units("")
X = R*np.cos(Theta)
Y = R*np.sin(Theta)
rho = frb["density"]

print("R:", minmax(R) )
print("Theta:", minmax(Theta) )
print("X:", minmax(X) )
print("Y:", minmax(Y) )
print("rho:", minmax(rho) )

slc.show()

plt.figure()
plt.imshow(rho)
plt.show()

plt.figure()
plt.hist( np.unique(Theta) )
plt.xlabel("Theta")
plt.ylabel("Counts")
plt.show()

I get this output:

R: (0.51171875, 1.98828125)
Theta: (0.012271846644580364, 6.270913635380566)
X: (-1.9881315382033238, 1.988131540336353)
Y: (-1.9881315392698402, 1.9881315371368034)
rho: (0.21301667392253876, 4.513450622558594)

Whereas I'd expect imshow to be similar to the slice plot and the histogram to be distributed over [0,2 pi]

[neutrinoceros]

thanks for pointing this out. I'll try to come back to see in a few days. In the meantime any additional feedback is most welcome.