Use om.Constraints throughout.

[hmgaudecker]

We still had the dict-based constraints from estimagic in here and converted to modern constraints only in the very last step. This PR switches to the optimagic constraints.

Main realisation: optimagic just picks whatever start value there is; but skillmodels needs to set the start value for fixed constraints. Hence we introduce a simple wrapper class:

@dataclass(frozen=True)
class FixedConstraintWithValue(om.FixedConstraint):
    """Fixed constraint that carries the target value and parameter location.

    `om.FixedConstraint` fixes parameters at their start values but does not carry a
    target value. This wrapper adds `loc` (the parameter location in the params
    DataFrame) and `value` (the value to set before optimization).
    """

    loc: pd.MultiIndex | tuple | str | None = None
    """Parameter location in the params DataFrame."""
    value: float | None = None
    """Value to enforce on the parameter."""

    def __post_init__(self) -> None:
        """Validate that `loc` and `value` are not None and derive `selector`."""
        if self.loc is None:
            msg = "loc must not be None"
            raise TypeError(msg)
        if self.value is None:
            msg = "value must not be None"
            raise TypeError(msg)
        object.__setattr__(
            self,
            "selector",
            functools.partial(select_by_loc, loc=self.loc),
        )

[codecov]

Codecov Report

❌ Patch coverage is 94.47853% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.86%. Comparing base (e965395) to head (da915d5).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/skillmodels/constraints.py	93.24%	5 Missing ⚠️
tests/test_constraints.py	93.61%	3 Missing ⚠️
src/skillmodels/transition_functions.py	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #86      +/-   ##
==========================================
- Coverage   97.04%   96.86%   -0.19%     
==========================================
  Files          57       57              
  Lines        4845     4809      -36     
==========================================
- Hits         4702     4658      -44     
- Misses        143      151       +8     

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