Fixes # .

Summary/Motivation:

• If a parameter has a nominal value of zero, we will get a divide by zero error when calling compute_FIM

Changes proposed in this PR:

• Added a minimum step size for perturbation.

TODO Before converting from draft

• Finish edits and debug
• Decide where to add check to throw error if we try to use parameter scaling and a parameter is zero
• Add tests to check this edge case include any new error message
• Update documenation (minor)

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.