Reevaluate all function and member names inside `numpy_usm_shared`

[diptorupd]

We should used leading underscores for all function and member names that are not intended to be exposed as part of the public API.

[PokhodenkoSA]

@diptorupd Is it possible to make it for the current release?

[diptorupd]

Should be a small task, but I may not get to it.

[diptorupd]

Closing as WONTFIX. numpy_usm_shared is under maintenance mode and will be deprecated once dpctl.tensor.usm_ndarray is more feature complete.