First prototype of aperture modelling functionality

[szymonlopaciuk]

Description

First prototype of the aperture modelling functionality. See examples/aperture_model/001_lhc_mqfa.py for an example usage.

Currently allows:

• Loading an aperture model from a line with limits, a line with MAD-X metadata, or a line with associated_apertures defined on elements.
• Calculation of the n1 using two different methods.
• Calculation of the beam envelope at arbitrary sigmas and pipe cross sections.
• Works in straight sections, and when profiles are not transformed w.r.t. their reference.

Currently not functional/under development:

• Correct handling of pipes in arcs.
• Correct interpolation (currently simply takes the nearest profile to the right).
• GPU untested, though OpenMP supported.

This is very much work in progress but could already be used in some scenarios.

Checklist

Mandatory:

• I have added tests to cover my changes
• All the tests are passing, including my new ones
• I described my changes in this PR description

Optional:

• The code I wrote follows good style practices (see PEP 8 and PEP 20).
• I have updated the docs in relation to my changes, if applicable
• I have tested also GPU contexts