Dwave-system

New Features
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* `LeapHybridDQMSampler`

Fixes
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* `embed_bqm` now always returns a BQM rather than sometimes returning a view

Changes
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- All samplers now strongly prefer either a QPU or a hybrid solver (288). See [Sampler behavior changes in 1.0.0](https://github.com/dwavesystems/dwave-system/wiki/Sampler-behavior-changes-in-1.0.0) for details.
- Removed deprecated `solver_features` kwarg in `DWaveSampler`
- Removed deprecated `order_by` kwarg in `DWave(Clique)Sampler`

New Features
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* New chain strength tuning methods, `uniform_torque_compensation` and `scaled`
* Embedding composites now use `uniform_torque_compensation` to set the default chain strength
* `MockDWaveSampler.sample` now accepts `**kwarg` for greater flexibility when testing

Fixes
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* `embed_bqm` no longer raises an error when `EmbeddedStructure` and `target_adjacency` are both provided. It now raises a deprecation warning

Fixes
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* Fix bug in `DWaveCliqueSampler` chain strength formula

Fixes
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* Improved chain strength calculation in `DWaveCliqueSampler`

New Features
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* `DWaveSampler.to_networkx_graph` method
* A faster implementation of `embed_bqm`
* A `EmbeddedStructure` class.
* Improved chain strength in `DWaveCliqueSampler`

Fixes
-----
* `DWaveCliqueSampler` now correctly supports legacy software solvers