[Code scan] Make find_neighbors handle mixed PrimitiveCell and SuperCell inputs

This issue comes from a Codex global scan of deepmodeling/tbplas at commit 4d3652b3dba8eb930e4869a6d41074f62d703692.

Severity: Medium

The signature allows `cell_bra` and `cell_ket` to be either `PrimitiveCell` or `SuperCell`, but the implementation dispatches position access mostly from the type of `cell_bra`. Mixed calls such as primitive-to-supercell or supercell-to-primitive can therefore call attributes/methods that do not exist on `cell_ket`.

Code reference:
https://github.com/deepmodeling/tbplas/blob/4d3652b3dba8eb930e4869a6d41074f62d703692/tbplas/builder/advanced.py#L402-L451

Suggested fix: resolve orbital positions independently for `cell_bra` and `cell_ket`, or narrow the accepted API and validate unsupported mixed-type calls explicitly.