added support and example for metastable isotopes

[dodu94]

Description

Metastable isotopes are now supported in reaction and irradiation files of D1SUNED through the addition of a '900' to their zaid identifier.

Type of change

Please select what type of change this is.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature
  • [ ] Non-breaking change which adds functionality
  • [ ] Breaking change fix or feature that would cause existing functionality to not work as expected

Other changes

• [ x ] This change requires a documentation update (only of jupyter notebooks)

Testing

New relevant tests have been added in the CI suite

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] General testing
  • [x] New and existing unit tests pass locally with my changes
  • [x] Coverage is >80%