feat: Add Complex Arithmetic Dataset and Tests

This commit introduces a new dataset for complex number arithmetic operations:

- Implements ComplexArithmeticDataset for generating complex number problems
- Supports addition, subtraction, multiplication, and division operations

Part of the algebra tasks collection in reasoning-gym.

tests/test_complex_arithmetic.py

@@ -0,0 +1,89 @@
+import pytest
+from reasoning_gym.algebra.complex_arithmetic import ComplexArithmeticConfig, ComplexArithmeticDataset
+
+
+def test_complex_arithmetic_basic():
+    """Test basic functionality of complex arithmetic dataset."""
+    config = ComplexArithmeticConfig(
+        min_real=-5,
+        max_real=5,
+        min_imag=-5,
+        max_imag=5,
+        operations=("+", "-", "*", "/"),
+        seed=42,
+        size=10
+    )
+    dataset = ComplexArithmeticDataset(config)
+    
+    print(dataset)
+
+    # Test dataset size
+    assert len(dataset) == 10
+    
+    # Test a specific item
+    item = dataset[0]
+    assert "question" in item
+    assert "answer" in item
+    assert "metadata" in item
+
+    # Add more detailed assertions
+    assert isinstance(item["question"], str)
+    assert isinstance(item["answer"], str)
+    assert isinstance(item["metadata"], dict)
+    
+    # Check metadata structure
+    assert "num1" in item["metadata"]
+    assert "num2" in item["metadata"]
+    assert "operation" in item["metadata"]
+    assert "result" in item["metadata"]
+    
+    # Check data types in metadata
+    assert isinstance(item["metadata"]["num1"], tuple)
+    assert isinstance(item["metadata"]["num2"], tuple)
+    assert len(item["metadata"]["num1"]) == 2  # Real and imaginary parts
+    assert len(item["metadata"]["num2"]) == 2
+    assert isinstance(item["metadata"]["operation"], str)
+    assert isinstance(item["metadata"]["result"], tuple)
+
+    # dump dataset into a text file 
+    with open("complex_arithmetic_dataset.txt", "w") as f:
+        for item in dataset:
+            f.write(str(item) + "\n")
+
+
+def test_complex_arithmetic_scoring():
+    """Test scoring function with various answer formats."""
+    config = ComplexArithmeticConfig(seed=42)
+    dataset = ComplexArithmeticDataset(config)
+    
+    # Create a test case with known answer
+    metadata = {
+        "result": (3.0, 2.0)  # represents 3 + 2i
+    }
+    
+    # Test various correct answer formats
+    assert dataset.score_answer("3 + 2i", metadata) == 1.0
+    assert dataset.score_answer("3+2i", metadata) == 1.0
+    assert dataset.score_answer("3.0 + 2.0i", metadata) == 1.0
+    
+    # Test incorrect answers
+    assert dataset.score_answer("2 + 3i", metadata) == 0.0
+    assert dataset.score_answer("3", metadata) == 0.0
+    assert dataset.score_answer("inf + 2i", metadata) == 0.0
+    assert dataset.score_answer("2i", metadata) == 0.0
+    assert dataset.score_answer("invalid", metadata) == 0.0
+
+
+def test_complex_arithmetic_division_by_zero():
+    """Test that division by zero is handled properly."""
+    config = ComplexArithmeticConfig(
+        operations=("/",),  # Only test division
+        seed=42
+    )
+    dataset = ComplexArithmeticDataset(config)
+    
+    # Check multiple items to ensure no division by zero
+    for i in range(10):
+        item = dataset[i]
+        num2 = complex(*item["metadata"]["num2"])
+        assert num2 != 0