The isNumeric function was rejecting valid hierarchical hash IDs like
'6we.2' that contain dots for parent.child notation. This caused
`bd import --rename-on-import` to fail with "non-numeric suffix" errors.
Changes:
- Rename isNumeric to isValidIDSuffix for clarity
- Accept dots (.) in addition to alphanumeric for hierarchical IDs
- Update test cases to cover hierarchical ID formats