Edges-cal

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Added
~~~~~

- New ``CompositeModel`` class that combines modular linear models and
behaves like a simple ``Model``.

Changed
~~~~~~~

- Fully reworked ``NoiseWaves`` class to use the ``CompositeModel``
class.

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Changed
~~~~~~~

- New ``model_filter`` function that ``xrfi_model`` calls and can be
called by other more general functions.

Added
~~~~~

- New tests of ``ModelFilterInfo`` and ``ModelFilterInfoContainer``

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Added
~~~~~

- New semi-rigid S-parameters file from 2017.

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Fixed
~~~~~

- Tests were slow because they were using the wrong default for getting
the standard deviation in ``xrfi_model``. Now uses the fast kind.

Changed
~~~~~~~

- ``modelling`` module got an overhaul. It now consists of smaller,
self-consistent classes that are based on ``attrs`` and are read-only
(but clonable). There is an explicit split between a ``Model`` and a
``FixedLinearModel`` which is defined at some coordinates ``x``,
allowing the latter to provide speedups for fitting lots of data at
the same coordinates. They are also YAML-read/writable.

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Added
~~~~~

- ``FourierDay`` linear model

Fixed
~~~~~

- models were being mutated in ``ModelFit``. No more.

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Added
~~~~~

- Ability to pass through LNA S11 options
- Ability to specify ``t_load`` and ``t_load_ns`` in spectra
- Easier conversion to ``Calibration`` object from
``CalibrationObservation``
- New ``NoiseWaves`` linear model
- Modular ``InternalSwitch`` class

Fixed
~~~~~

- Ensure fitted models are always copied