Fix Rosenbrock MINUS_ONE bug

[alexander-novo]

Description

Rosenbrock was using wrong value of alpha when evaluating model Jacobian - there was an extra minus sign. This wasn't caught by the test because the test was also incorrectly using alpha in its own Jacobian - there was a missing minus sign. These cancelled out and cause correct behavior when Rosenbrock was applied to the test problem.

Some documentation has been added to assist with understanding the issue.

Proposed changes

The MINUS_ONE in Rosenbrock's model Jacobian evaluation has been changed to a ONE, and the test has been updated to compute its Jacobian in a way that agrees with the rest of GridKit.

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 compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ 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.
• 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.

This is a fix to the rosenbrock integrator, which is already included in the changelog

Further comments