v1.3.0

Title
Release v1.3.0

Body
This release merges develop into main for v1.3.0.

Changes since v1.2.5 include:

• Nonlinear optics and RDT improvements

  • Extended Twiss output with chromatic optics quantities for both AT and Xsuite backends. get_twiss() now exposes chromatic beta, alpha, phase, and dispersion fields, including wx_chrom, bx_chrom, ax_chrom, wy_chrom, by_chrom, ay_chrom, dmux, dmuy, and ddx.
  • Updated RDT feeddown calculations to use the revised sign convention (-r0) ** (k - n).
  • Improved integrated-strength feeddown handling by averaging the closed orbit across element entrance and exit, applying roll as exp(-i*roll), and documenting that returned strengths follow the MAD-X/Xsuite/PALS convention.
  • Moved RDT optics and phase evaluation to element-center averages: hjklm() now uses averaged beta functions and fjklm() uses averaged phase advances between adjacent reference points.
  • Added and updated tests for the new chromatic Twiss fields and RDT convention changes.

• Sextupole BBA support

  • Added support for beam-based alignment using the sextupolar field component of a magnet, alongside existing normal and skew quadrupole BBA workflows.
  • Introduced a MagnetType enum to identify magnet components at runtime, including normal quadrupoles, skew quadrupoles, normal sextupoles, dipoles, octupoles, and undefined components.
  • Generalized BBA measurement configuration from the previous quadrupole/skew-quadrupole model to a magnet_type based model, while keeping deprecated compatibility handling for older quad_is_skew / skew_quad usage.
  • Updated BBA analysis to use linear fits for quadrupoles and quadratic fits for sextupoles, extracting the sextupole alignment center from the quadratic minimum.
  • Improved orbit and trajectory BBA configuration generation for sextupoles, including sextupole-specific modulation and BPM displacement limits, optional sextupole filtering, and validation when no BBA magnets remain after filtering.
  • Made trajectory-based BBA configuration more robust by using an analytical first-order trajectory response estimate from Twiss beta and phase data instead of relying only on sampled response-matrix slices.
  • Added tests covering sextupole BBA configuration, measurement setup, magnet typing, orbit BBA, trajectory BBA, and tuning-core behavior.

• Added tune scan and synchrotron energy correction tuning methods.

• Added BPM gain corrections, particle count configuration, and transmission return support.

• Added generic lattice file support via at.load_lattice.

• Added sklearn method plugin support.

• Added a comprehensive unit test suite and test workflow.

• Improved backward compatibility for BPM field initialization.

• Fixed bugs in RF configuration scope, RF response weighting, transmission threshold propagation, support configuration checks, and linear_normal_form.

• Tightened Pydantic model validation with extra="forbid".