Clean up class ExampleHelper

[pelesh]

Description

Simplify class ExampleHelper and remove redundant code.

Proposed changes

• Remove set and reset helper functions.
• Print summary functions now compute all norms before printing.
• GMRES solvers now return relative residual instead of absolute residual.
  • GMRES solvers still use absolute residual for exit criteria; this needs to be addressed separately from this PR.
• Modified examples to use simplified ExampleHelper class.

Checklist

• All tests pass (make test and make test_install per testing instructions). Code tested on
  • CPU backend
  • CUDA backend
  • HIP backend
• I have manually run the non-experimental examples and verified that residuals are close to machine precision. (In your build directory run:
  ./examples/<your_example>.exe -h to get instructions how to run examples). 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.
• N/A 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

[KakeruUeda]

Tested on CUDA backend. All tests passed and examples ran successfully.

[shakedregev]

Looks good, approved.
Tests pass on CUDA, HIP, and CPU. Please fix the minor comment issue.