add unit tests for complex numbers

[Haydn Vestal]

This should include tests for basic math operations between:

• one complex number
• two complex numbers
• one complex and one real number
• one complex tensor
• one complex tensor and one complex number
• one complex tensor and one real number
• two complex tensors
• one complex tensor and one real tensor

There are examples to follow here: https://github.com/haydnv/tinychain/blob/main/tests/tctest/host/test_tensor.py