Stop carrying bodyless Rust declarations into the next impl #866

Problem

The spacing helper treated a semicolon-terminated trait function declaration as an unfinished function and carried it into the following impl, producing spacing that disagreed with rustfmt.

Reproduction

At the pre-fix formatter, feed a trait containing fn run(); followed by impl Trait for Type. Check function_ranges/add_function_spacing. PR #860 clears bodyless declarations on their terminating semicolon; smoke checks cover this case and idempotence.

Implementation status: Already implemented in open PR #860. This issue restores missing tracking; do not duplicate the implementation. Review and final PR validation remain with that PR.

Completion criteria

• Recognize bodyless trait/extern declarations without borrowing a later body.
• Keep formatting idempotent and consistent with rustfmt.