- Modified the initial beam size in the IOTA lens benchmark example.
- Added 2 benchmarks of 3D space charge for initial testing.
- Add documentation for 2 benchmarks with space charge.
- Add a benchmark example with space charge and periodic s-dependent focusing.
- Added an s-dependent example using a Kurth beam without space charge.
- Modified tolerance for IOTA lens benchmark example.
  Reduced tolerance to account for smaller initial beam size and
  improved preservation of invariants of motion.
- Modified tolerances of space charge examples to allow CI tests to
  pass when space charge is not active.

- Modified tolerance for space charge examples.
  These should fail unless space charge is turned on.

Selected numerical values for amr.n_cell, lattice.nslice, and geometry.prob_relative.

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Relax tolerance.