Xtrack version 0.97.1

Changes:

• Generalize RBend to support arbitrary orientation and shift. Added attributes: rbend_compensate_sagitta, rbend_angle_diff #729 .
• Updates in documentation #726 and #728.
• Further the implementation of include headers functionality #714:
  • Register headers for Xtrack the same way as the other packages (through the hook in pyproject.toml). This means the headers can also (and in the future should only) be included with #include "xtrack/..." without assuming xtrack is top-level. This is to avoid collisions with the other Xsuite packages. In the future the old way should be disabled.
  • Update the examples to use the new way.
  • Populate properly the pyproject.toml file. We can remove setup.py while still using setuptools, as it's not doing anything special currently.
  • Bump the supported Python version to 3.9+.
  • Move atomicAdd and qualifier keyword macros to Xobjects (see xsuite/xobjects#160).
  • Implement what we can with headers (e.g. multisetter.h, local_particle_custom_api.h)
  • Get rid of the magic comment /*placeholder_for_local_particle_src*/ and the related behaviour (the functionality was unnecessarily convoluted as a result of ParticlesPurelyLongitudinal -- it is now simpler, is fact no need to regenerate and propagate local_particle_src as it's completely static in the current version of Xsuite).
  • The above also indirectly fixes a bug where /*placeholder...*/ would be ignored if the same snippet of code didn't contain //start_per_particle_block.

Full Changelog: v0.97.0...v0.97.1