taichi

As shown in taichi-dev/taichi#3910, replacing property with simple attributes can speedup python part of taichi a lot.
Lessons learned is that we should avoid using @property when applicable since it's expensive. So let's review the usage of @property in our python codebase and replace them as much as possible.

Here's a list of simple grep in our codebase showing

Now stannum (and generally Taichi) cannot do automatic batch as done in PyTorch.

For example, the below can only handle 3 arrays, but if we have a batch of arrays, we will have to loop over the batch dimension or change the code to support batches of a fixed size. This issue is somewhat related to issue #5. The ultimate goal should be supporting automatic batching with tensors of valid flexi