Xfields

**Changes:**
- Add computation of IBS growth rates.
- Reorganize beam beam 3d code.

**Full Changelog**: https://github.com/xsuite/xfields/compare/v0.15.1...v0.16.0

**Changes:**
- Adapt to new Xtrack behavior on json load
- Faster beam-beam element insertion

**Full Changelog**: https://github.com/xsuite/xfields/compare/v0.15.0...v0.15.1

**Changes:**
- Introduce `FFTSolver2p5DAveraged`
- In space charge config tool keep the line buffer and get particle_ref from line when possible.
- Switch to fast element insertion in spacecharge tools.

**Full Changelog**: https://github.com/xsuite/xfields/compare/v0.14.2...v0.15.0

**Changes:**
- Prepare for `FFTSolver2p5DAveraged` implementation.

**Full Changelog**: https://github.com/xsuite/xfields/compare/v0.14.1...v0.14.2

**Changes**
- Introduce fast slicer based on shared memory for BB3D.
- Improvements in beamstrahlung and Bhabha

**Full Changelog**: https://github.com/xsuite/xfields/compare/v0.14.0...v0.14.1

**Changes:**
- Introduce strong-strong mode in `BeamBeamBiGaussian2D`.
- Better testing for strong-strong beam beam (including pipeline).
- Fix in `spacecharge_config_tools`

**Full Changelog**: https://github.com/xsuite/xfields/compare/v0.13.1...v0.14.0