Add expression component

[henrikjacobsenfys]

So that users can easily define their own models.
Example:

        expr = ExpressionComponent(
            "A * exp(-(x - x0)**2 / (2*sigma**2))",
            parameters={"A": 10, "x0": 0, "sigma": 1},
        )

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.83%. Comparing base (cec1976) to head (d29f314).
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@@             Coverage Diff             @@
##           develop     #143      +/-   ##
===========================================
+ Coverage    97.75%   97.83%   +0.07%     
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===========================================
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  Partials        24       24              

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[rozyczko]

I think you need to address an unknown function issue.

[rozyczko]

There is no post-parse validation that all function calls are in the allowlist.
E.g.
ExpressionComponent("foo(x)") will initialize successfully, but evaluate raises NameError when calling self._func(*args)
Is this as designed?

>>> from easydynamics.sample_model import ExpressionComponent as ec
>>> expr = ec("foo(x)")
>>> expr.evaluate(1)
  File "C:\projects\easy\dynamics-lib\src\easydynamics\sample_model\components\expression_component.py", line 198, in evaluate
    return self._func(*args)
           ^^^^^^^^^^^^^^^^^
  File "<lambdifygenerated-1>", line 2, in _lambdifygenerated
NameError: name 'foo' is not defined

[rozyczko]

How about a simple validator?

        # Reject unknown functions early so invalid expressions fail at init,
        # not later during numerical evaluation.
        allowed_function_names = set(self._ALLOWED_FUNCS) | {
            func.__name__ for func in self._ALLOWED_FUNCS.values()
        }

        # Walk all function-call nodes in the parsed expression (e.g. sin(x), foo(x)).
        # Keep only function names that are not in our allowlist.
        unknown_function_names: set[str] = set()
        function_atoms = self._expr.atoms(sp.Function)
        for function_atom in function_atoms:
            function_name = function_atom.func.__name__
            if function_name not in allowed_function_names:
                unknown_function_names.add(function_name)

        unknown_functions = sorted(unknown_function_names)

        if unknown_functions:
            raise ValueError(
                f"Unsupported function(s) in expression: {', '.join(unknown_functions)}"
            )

This will show a much more informative

>>> e = ec('foo(x)')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\projects\easy\dynamics-lib\src\easydynamics\sample_model\components\expression_component.py", line 128, in __init__
    raise ValueError(
ValueError: Unsupported function(s) in expression: foo

[henrikjacobsenfys]

Very good point! I somehow did not consider this case, not even when playing around with the implementation to see if it was robust.

[rozyczko]

This now looks good.
But it would be also useful for others to have a look