Fix inner data type in interval scorer and unify cost names

[Tveten]

• Fixes [MNT] Fix inner data type handling in interval scorers #48.
• Unify naming of parametric likelihood-based costs/scores:
  • Change GaussianVarCost -> GaussianCost.
  • In line with Specialize gaussian cov change score to add Bartlett correction #38, which changes GaussianCovCost -> MultivariateGaussianCost.
  • General naming convention:
    • Add Multivariate prefix to multivariate costs.
    • Don't add Univariate in front of univariate costs. These are so common that it can be implicit.
    • Names like GaussianVarCost or GaussianMeanCost means that the cost only considers the var or mean.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.50%. Comparing base (a7c2d2c) to head (37603a0).
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #50      +/-   ##
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- Coverage   97.53%   97.50%   -0.04%     
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  Files          40       40              
  Lines        1701     1680      -21     
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- Hits         1659     1638      -21     
  Misses         42       42              

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