Xtrack

**Changes:**
- Introduce computation of equilibrium emittances in the result of `twiss(..., ene_loss_and_damping=True)`.
- Introduce `Line.match(compensate_radiation_energy_loss=True)`.
- Introduce `Line.vv` as alias of `Line.varval`.
- Introduce `Line.attr` for quick extraction of commonly used element attributes (length, hxl, hyl, low order strengths).
- Introduce backtrack for `CombinedFunctionMagnet`.
- Introduce `Line.metadata` and `Multiline.metadata`.
- Introduce `Target(..., optimize_log=True)` flag to optimize the logarithm of a quantity.
- Introduce support for `Int64` attributes in `Multisetter`.
- Introduce `TwissInit.to_dict(...)`, `TwissInit.from_dict(...)`, `TwissInit.to_json(...)`, `TwissInit.from_json(...)`.
- Refactor prebuilt kernel management to control the order in which they are checked.
- Refactor `Line.compensate_radiation_energy_loss()` to preserve expressions. New implementation is also considerably faster.
- Switched to `radiation_method = "kick_as_co"` as default in the presence of radiation (significantly faster than `full`).
- Fix sign error on weak focusing from `hyl` in multipole.
- In mad_loader, add entry and exit markers also for thin elements that are not markers themselves.
- Use shorter suffix when splitting drifts to insert elements.
- Performance improvement in `line.__getitem__`.
- Improved speed in `LastTurnMonitor`.

**Full Changelog**: https://github.com/xsuite/xtrack/compare/v0.40.2...v0.41.0

**Changes:**
- Introduce `NonLinearLens` element (based on MAD-X `nllens`).

**Full Changelog**: https://github.com/xsuite/xtrack/compare/v0.40.1...v0.40.2

**Changes:**
- Introduce `ParticlesMonitor.to_dict` and `ParticlesMonitor.from_dict` methods.

**Full Changelog**: https://github.com/xsuite/xtrack/compare/v0.40.0...v0.40.1

**Changes**
- Introduce `only_markers` mode for `Line.twiss`.
- In `Line.twiss` finite-difference steps are automatically adapted to estimated beam size.
- New feature in `Line.match`
- `xtrack.START` and `xtrack.END` can be used as location in match targets.
- `TargetSet` can be used to specify multiple parameters at the same location.
- Default values for vary limits and steps can be specified in `Line.vars.vary_default`.
- `Line.match` always returns the optimizer object.
- Add examples of rematching for LHC optics.

**Full Changelog**: https://github.com/xsuite/xtrack/compare/v0.39.0...v0.40.0

**Changes**
- New capabilities related to element compounds:
- Insertion of elements within compounds.
- Slicing of thick elements within compounds with propagation to all slices of the aperture and related tilts and shifts.
- New feature in matching with generation of an optimizer object to inspect and drive the matching process (the object can be obtained with `optimizer = line.match(solve=False)`). The optimizer object allows the following actions:
- Perform an assigned number of optimization steps calling `optimizer.step(...)`.
- Iterate until solution is found or termination condition is met through `optimized.solve(...)`.
- Disable/enable targets and vary objects through their `active` flag.
- Inspect vary's and targets of the optimizer using the method `optimizer.show()`.
- Assign a tag to groups of vary's and targets and disable/enable groups by calling `optimizer.disable_targets(tag=...)`, `optimizer.disable_vary(tag=...)`, `optimizer.enable_targets(tag=...)`, `optimizer.enable_vary(tag=...)`.
- Inspect the optimizer iteration history through `optimizer.log()`. History can be deleted by `optimizer.clear_log()`
- Reload the state from a given iteration by calling `optimizer.reload(...)`.
- Provide defaults for vary steps and limits through `Line.vars.vary_default`.
- Provide defaults for target tolerances through `match(default_tol={...}`.
- Expose all features above in the matching of knobs.
- Introduced `Line.vars.load_madx_optics_file` method.
- Introduce `Line.varval` to easily access variable values (`line.varval['a']` equivalent to `line.vars['a']._value`)
- Introduce backtracking for thick elements `Quadrupole` and `Bend` (the latter only in expanded mode).
- Introduce `Multiline.copy()` method.
- Introduce method `TwissTable.concatenate` to concatenate twiss tables.
- Introduced `TargetRelPhaseAdvance` to match relative phase advance between two points.
- Fix handling of custom twiss_init when `twiss_default['reverse']` is `True`.

**Full Changelog**: https://github.com/xsuite/xtrack/compare/v0.38.3...v0.39.0

**Changes:**
- Fix in dipole wedge map (issue with ions)
- Add `Tracker._init_io_buffer` method.

**Full Changelog**: https://github.com/xsuite/xtrack/compare/v0.38.2...v0.38.3