Fixed double allocations and added assert statements

[shakedregev]

Description

Error messages are returned when running GMRES tests suggesting the solver is trying to access GPU memory. These are benign messages as computation is carried out to completion on a CPU device and all GPU calls are ignored, but the code should not be trying to access the the device memory in the CPU mode in the first place.

_Closes #286 _

@pelesh

Proposed changes

My changes enforce strict checks on owning gpu data and remove double allocations.

Checklist

Put an x in the boxes that apply. You can also fill these out after creating
the PR. If you're unsure about any of them, don't hesitate to ask. We're here
to help! This is simply a reminder of what we are going to look for before
merging your code.

• All tests pass. Code tested on
  • CPU backend
  • CUDA backend
  • HIP backend
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows Re::Solve style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.

The rebase was required to get tests passing.

[pelesh]

Build and installation tests pass, straightforward fix.