Interface for objects that can be reused different Placements about moose

[jvmncs]

This issue was referring to the old Python prototype. IIRC we were informally handling values we could represent in computations via soft requirements in the (Python) kernels for load, constant, and input ops. Now the requirements for what values can be used in computations is informally handled by the msgpack helper code (both python and rust) that handle serde from pymoose into moose. So we don't yet have a tidy interface for this, but also the situation is more bearable because error messages for using non-handled types are made much more obvious. I think we can continue to improve this situation as we refactor/improve pymoose in work covered by other issues.

Verdict: I would vote to either close this issue or rewrite it to more clearly define what it would look like in the current version of the code.