feat: add Choice class for possible values of hyperparameter (#325)

### Summary of Changes

Add a class to represent possible choices for the value of a
hyperparameter. This is in preparation for #264.

src/safeds/ml/hyperparameters/__init__.py

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+"""Tools to work with hyperparameters of ML models."""
+
+from ._choice import Choice
+
+__all__ = ["Choice"]

src/safeds/ml/hyperparameters/_choice.py

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+from __future__ import annotations
+
+from collections.abc import Collection
+from typing import TYPE_CHECKING, TypeVar
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
+    from typing import Any
+
+T = TypeVar("T")
+
+
+class Choice(Collection[T]):
+    """A list of values to choose from in a hyperparameter search."""
+
+    def __init__(self, *args: T) -> None:
+        """
+        Create a new choice.
+
+        Parameters
+        ----------
+        *args: tuple[T, ...]
+            The values to choose from.
+        """
+        self.elements = list(args)
+
+    def __contains__(self, value: Any) -> bool:
+        """
+        Check if a value is in this choice.
+
+        Parameters
+        ----------
+        value: Any
+            The value to check.
+
+        Returns
+        -------
+        is_in_choice : bool
+            Whether the value is in this choice.
+        """
+        return value in self.elements
+
+    def __iter__(self) -> Iterator[T]:
+        """
+        Iterate over the values of this choice.
+
+        Returns
+        -------
+        iterator : Iterator[T]
+            An iterator over the values of this choice.
+        """
+        return iter(self.elements)
+
+    def __len__(self) -> int:
+        """
+        Get the number of values in this choice.
+
+        Returns
+        -------
+        number_of_values : int
+            The number of values in this choice.
+        """
+        return len(self.elements)

tests/safeds/ml/hyperparameters/test_choice.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+import pytest
+from safeds.ml.hyperparameters import Choice
+
+if TYPE_CHECKING:
+    from typing import Any
+
+
+class TestContains:
+    @pytest.mark.parametrize(
+        ("choice", "value", "expected"),
+        [
+            (Choice(1, 2, 3), 1, True),
+            (Choice(1, 2, 3), 2, True),
+            (Choice(1, 2, 3), 3, True),
+            (Choice(1, 2, 3), 4, False),
+            (Choice(1, 2, 3), "3", False),
+        ],
+        ids=[
+            "value in choice (start)",
+            "value in choice (middle)",
+            "value in choice (end)",
+            "value not in choice",
+            "value not in choice (wrong type)",
+        ],
+    )
+    def test_should_check_whether_choice_contains_value(self, choice: Choice, value: Any, expected: bool) -> None:
+        assert (value in choice) == expected
+
+
+class TestIter:
+    @pytest.mark.parametrize(
+        ("choice", "expected"),
+        [
+            (Choice(), []),
+            (Choice(1, 2, 3), [1, 2, 3]),
+        ],
+        ids=[
+            "empty",
+            "non-empty",
+        ],
+    )
+    def test_should_iterate_values(self, choice: Choice, expected: list[Any]) -> None:
+        assert list(choice) == expected
+
+
+class TestLen:
+    @pytest.mark.parametrize(
+        ("choice", "expected"),
+        [
+            (Choice(), 0),
+            (Choice(1, 2, 3), 3),
+        ],
+        ids=[
+            "empty",
+            "non-empty",
+        ],
+    )
+    def test_should_return_number_of_values(self, choice: Choice, expected: int) -> None:
+        assert len(choice) == expected