Add float32 constructor to complex64

stdlib/internal/types/complex.codon

@@ -300,6 +300,9 @@ class complex64:
     def __new__(other):
         return complex64(other.__complex__())
 
+    def __new__(real: f32):
+        return complex64(real, f32(0.0))
+
     def __new__(other: complex) -> complex64:
         return (f32(other.real), f32(other.imag))
 

test/stdlib/cmath_test.codon

@@ -826,4 +826,17 @@ def test_complex64():
     assert hash(z)
     assert c64(complex(z)) == z
 
+    z = c64(1.5, 2.5)
+    assert z.real == f32(1.5)
+    assert z.imag == f32(2.5)
+    z = c64(3.5)
+    assert z.real == f32(3.5)
+    assert z.imag == f32(0.0)
+    z = c64(f32(4.5), f32(5.5))
+    assert z.real == f32(4.5)
+    assert z.imag == f32(5.5)
+    z = c64(f32(6.5))
+    assert z.real == f32(6.5)
+    assert z.imag == f32(0.0)
+
 test_complex64()