Accurate read RZ representation from openPMD file to LASY

[MaxThevenet]

This class

lasy/lasy/profiles/from_openpmd_profile.py

Line 12 in 2c1f249

class FromOpenPMDProfile(FromArrayProfile):

can read from an openPMD file. Nevertheless, when using LASY in RT mode the data is assumed axisymmetric although LASY can in principle handle azimuthal mode decomposition. Rather than taking a cut at a given $\theta$, as currently done, I think the correct conversion between the modes of the full electric field in an openPMD file (as written by FBPIC for instance) and those used for the envelope in LASY is

where $p_x=1$ for linear polarization in $x$, $\mathcal{E}^m$ is mode $m$ in LASY and $E_{r/\theta}^m$ is mode $m$ in FBPIC for $E_{r/\theta}$. Here, $i$ is the imaginary number. This should be implemented in the class mentioned above.

Additionally, reading all modes from the openPMD data should be done with openPMD-api instead of openPMD-viewer, so the dependency on openPMD-viewer can be dropped entirely. The operations should be symmetric to what is done in

lasy/lasy/utils/openpmd_output.py

Line 12 in 2c1f249

def write_to_openpmd_file(