Update adapter defaults

[matt-graham]

• Changes default behaviour of sample_chain function to be to use dual averaging scale adapter and dense covariance shape adapter.
• Adds two new functions scale_adapter and shape_adapter which wrap the algorithm specific variants.
• Changes variance and covariance shape adapters to defaulting to using kappa = 1 corresponding to empirical (co)variance updates.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (4996fa3) to head (83abf52).
Report is 8 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files           11        11           
  Lines          521       533   +12     
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+ Hits           521       533   +12     

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