Xtrack version 0.96.0

Changes:

• Implement Environment.vars.rename(…)
• `xt.load(…) supports a list of mad files.
• Add s_tol and and _rbend_correct_k0 options to xt.load().
• Mark autogenerated drifts ad ||drift_XX and reuse them when possible. No DriftSlice element is created when these drifts are sliced.
• Preserve last context when rebuilding trackers without passing context or buffer.
• In LimitPolygon avoid enforcing anti-clockwise ordering of vertices.
• Fix issue in LossLoacationRefinement
• Fixes in MAD-X writer, MAD-NG interface and native MAD-X loader.

Full Changelog: v0.95.0...v0.96.0