Xtrack version 0.73.0

Changes:

• Fix in emittance calculation with solenoids
• Ability to slice repeated elements.
• Added a summary of key methods and attributes in the Environment class docstring.
• Anchors in line definitions:
  • env.new_line() and Builder now support anchors (env.place and env.new accept a parameter anchor valued start, end, center).
  • Enabled placement of sub-lines and handling of thin elements with clear ordering.
• Line-editing methods:
  • Introduced new Line methods: insert, append, remove, and replace.
  • Deprecated Line.insert_element and Line.append_element in favor of new methods.
  • Unified API behavior with Builder for consistency.
• Deprecation of Multiline in favour of Environment:
  • Extended Environment to handle all use cases of the deprecated Multiline.
  • API backward compatibility ensured
  • Automatic conversion of old Multiline JSON to Environment to ease transition.
  • Introduced renaming for shared elements (e.g., 'mqxfa.a1r1/lhcb1').
  • Marked Multiline for removal within 1–2 months, pending user communication and JSON re-saving.
• Apply fixes and relax some tolerances in tests after a new release of SciPy changes some of the constants in scipy.constant.

Full Changelog: v0.72.2...v0.73.0