Add batching of evidence estimation inputs and update examples

[alicjapolanska]

• Add functionality to batch samples for evidence estimation in the add_chains method to avoid memory issues.

• Change Rosenbrock example to be able to handle arbitrary dimension and fix bugs.

• Switch Gaussian example and plotting of realisations to log space.

[CosmoMatt]

@alicjapolanska A few points raised, all super small, I've approved either way whether you make these changes or not. Good stuff sorting this problem :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.80%. Comparing base (9726ce2) to head (16b72d5).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #307      +/-   ##
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+ Coverage   95.73%   95.80%   +0.06%     
==========================================
  Files          14       14              
  Lines        2298     2335      +37     
==========================================
+ Hits         2200     2237      +37     
  Misses         98       98              

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