Dwave-system

Fixes
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* `LeapHybridSampler` now correctly chooses solvers that accept the `bqm` problem type

New Features
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* Biclique support for Pegasus

New Features
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* `unembed_sampleset` now accepts multiple chain break resolution methods

Fixes
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- Fixed QUBO sampling bug in `DWaveSampler` introduced in 0.9.2 (286)

Fixes
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* Install `dwave-tabu` which is needed for the `dwave.system.testing` module

New Features
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* Updated documentation
* `LeapHybridSampler` and `DWaveSampler` both now make use of the cloud client's `Future.sampleset` attribute
* `LeapHybridSampler` no longer blocks
* `DWaveSampler.sample` no longer blocks
* `LeapHybridSampler` now sets `client=base` by default

Fixes
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* Fixed warning descriptions to be more consistent
* `embed_bqm` now raises a `MissingChainError` when provided with zero-length chains

Support dwave-cloud-client 0.7.x