Beam-Beam Kernel with test

[RevanEoot]

• Added beam-beam kernel
• Added SpecialFunctions and Roots for beam-beam tracking
• Added a single test

The current tests are failing, so I will continue to update until tests pass.

[RevanEoot]

Current tests are off by a lot from Bmad. I'm trying to find where the numbers are deviating, but I suspect it's coming from the collision point calculation.

[RevanEoot]

Fixefdbeambeam kernel and added extensive tests for particle tracking. The tests don't always pass for phase space z due to a problem with the exact_drift kernel.
I will soon have tests for the TPS functionality.
I will also be adding the crossing angle.

[mattsignorelli]

Can you provide a minimal working example (no beam-beam) where exact_drift disagrees with Bmad?

[RevanEoot]

Collision point calculation now uses a formula rather than root finder and all tests are passing. TPS tracking agrees on zero orbit, but disagrees off the zero orbit. This is likely a result of something within the kick calculation, but I don't know the exact origin at the moment.