Add sysGmres example

[KakeruUeda]

Description

This adds an example that solves a linear system with GMRES through the SystemSolver interface in ReSolve, demonstrating how to use it in user applications.

Closes #400

Proposed changes

• Add a new example source file example/sysGmres.cpp.

Note: The HIP backend has not been tested yet, as HIP is not available in my current setup.

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.
• N/A There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

I would appreciate any help with testing this example on the HIP backend.

[pelesh]

Tested on HIP backend and all tests passed. Ran the sysGmres.exe example on a HIP backend and had system converge.

[pelesh]

Please update the changelog. Otherwise ready to merge.

[KakeruUeda]

Thank you. I've updated the changelog.