add Matrix66RadPass passmethod

[swhite2401]

This PR adds a Matrix66RadPass passmethod to allow switching radition on or off for an M66 element using the standard enable_6d/disable_6d function.

This is the first step to a complete refurbishment of the fastring module.

This is for the comment a proposal, any comments or suggestions are more than welcome.

[swhite2401]

Test script:

import at
import numpy as np
import matplotlib.pyplot as plt

ring = at.load_lattice("../lattice/hmba.mat", periodicity=1)
cavs = ring.get_uint32_index(at.RFCavity)
newring = []
allcavs = []
for ii, ic in enumerate(cavs[::-1]):
    print(ii, ic)
    allcavs.append(ring[ic])
    if ic < len(ring):
        ring = ring[:ic]+ring[ic+1:]
    else:
        ring = ring[:ic]
ring = ring.repeat(32)
ring += allcavs
ring.rf_voltage = 5.5e6
ring.set_rf_frequency()

print(ring.enable_6d(copy=True).envelope_parameters())

ring_norad = ring.disable_6d(copy=True)
ring_norad.enable_6d(at.RFCavity)
ring_rad = ring.enable_6d(copy=True)

m66 = at.gen_m66_elem(ring_norad, ring_rad)

fring = at.Lattice([m66], energy=ring.energy)

fring.disable_6d()
pout, *_ = fring.track(np.ones(6)*1e-4, nturns=10000)
pout=np.squeeze(pout)

plt.subplot(231)
plt.plot(pout[0,:], pout[1,:], '.')
plt.subplot(232)
plt.plot(pout[2,:], pout[3,:], '.')
plt.subplot(233)
plt.plot(pout[5,:], pout[4,:], '.')

fring.enable_6d()
pout, *_ = fring.track(np.ones(6)*1e-4, nturns=10000)
pout=np.squeeze(pout)

plt.subplot(234)
plt.plot(pout[0,:], pout[1,:], '.')
plt.subplot(235)
plt.plot(pout[2,:], pout[3,:], '.')
plt.subplot(236)
plt.plot(pout[5,:], pout[4,:], '.')

plt.tight_layout()
plt.show()

Result:

[swhite2401]

@lfarv @lcarver I believe this is ready for review. I will start the new fastring development based on this in a new branch.