Add first above threshold aggregation

[MahmoodEtedadi]

Overview

Closes #136

Description of changes

Author Checklist

• [ ] Linting passes; run early with pre-commit hook.
• [ ] Tests added for new code and issue being fixed.
• [ ] Added type annotations and full numpy-style docstrings for new methods.
• [ ] Draft your news fragment in new changelog/ISSUE.TYPE.rst files; see changelog/README.md.