Rust bindings does not encode non-zero line invariant from C API

[cijiugechu]

The C/C++ API documents line numbers as 1-based, with 0 reserved as an error sentinel.
However, the Rust binding currently models lines as plain u32 in public data structures, so the non-zero invariant is not fully encoded in types.

[anonrig]

I think this can be closed now.