Create a class to model Circular Buffers

[jakedves]

Create a class to model Circular Buffers.

Some things that may be useful:

• reading from it (return type? Grid)
• writing to it
• storing an index to use (1..16)

We never run the code so index must be determined at compile-time, so PythonToMLIR object should be the one tracking instantiations rather than the circular buffer itself.

def func(a: CircularBuffer, b: CircularBuffer):
    a.read()  # read default size from circular buffer index 1? 
    a = b
    a.read()  # read .. index 2? 

Valid code above? Can choose. Could make it a rule (=> error) that circular buffers must only be referenced by their parameter name, or could allow dynamism but then can't just use a var_name -> CBIndex map in PythonToMLIR. First case is simpler and should cover most, if not all, programs.