Gapless beam pipe vacuum

[simonge]

Briefly, what does this PR introduce?

Changes the beampipe chain so it no longer adds a small air gap when there is a bend in the pipe and instead joins them together properly with a torus segment.

Exaggerated geometry pictures showing the difference between current and new implementation.

The previous implementation was sufficient to remove the overlaps when the bend has a very small angle and small radius, but a small air gap in the vacuum isn't ideal even then.

Motivation for introducing this is that to update the backwards beamline magnets to match the current lattice a bend needs to be added. Currently I believe these bends in the beampipe chain are only present in material we don't care about tracking particles through.

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No

Does this PR change default behavior?

Should remove small amounts of air from bending beamline chains with bends.