Resolves the OmegaConf interpolations Monty's configs are written in.

Composition leaves ${...} strings exactly as Monty's snapshots have them; this module turns them into values:

${constants.min_eval_steps}                     a reference into the tree
${oc.env:MONTY_DATA}                            an environment variable
${oc.env:MONTY_DATA,/tmp/data}                  ... with a default
${monty.class:tbp.monty.geometry.Rotation}      a class reference
${np.array:[2, 0.5, 0.5]}                       a numeric array
${np.ones:3}                                    [1.0, 1.0, 1.0]
${np.list_eval:[np.pi / 8, np.pi * 2]}          arithmetic
${path.expanduser:~/tbp/data}                   ~ expanded
${path.tests:fixtures/cube.json}                inside Monty's tests/

monty.class deserves a note: Monty returns the class object, which an Elixir process cannot hold. This returns the dotted path as a string and leaves the mapping to an Elixir module to Monty.Config.Registry, so the config file stays readable and an unknown class stays visible instead of blowing up during composition.