fix: resolve ruff 0.15.0 lint violations

[r-dh]

Fix lint violations flagged by ruff 0.15.0

• Simplify lambda x: chunk_spans.extend(x) to chunk_spans.extend (unnecessary lambda)
• Replace x if x else y with idiomatic x or y
• Remove redundant outer parentheses in expression
• Move ChunkSpan import behind TYPE_CHECKING guard

All changes are mechanical lint fixes, there are no logic changes.

[emilradix]

@r-dh What order should I merge this and #175 in? I propose merging this and then you get rid of the ruff pin in #175?

[r-dh]

That works for me!

[emilradix]

LGTM