IntParam value type change due to attribute writeback

[dnadlinger]

There might be more than one root cause here, but we have observed annoying compilation failures due to the value type of IntParams changing after the first of several kernel executions due to attribute writeback. Specifically, the host-side value type was first a Python built-in int, and got inferred as a TInt32, but after the kernel exited, became a numpy.int64 on the host.

Possible solutions:

• Fix attribute writeback – it's unclear why it should lead to the type being widened.
• Always hard-code IntParamStore type to numpy.int32.