v4: `api:extract` keeps imports of symbols it trimmed as `@internal`

[barjin]

API Extractor collects the import list before dropping non-@public declarations and never revisits it, so a symbol referenced only by @internal members lingers as an import and reads as public API - e.g. docs/public-api/crawlee-core.api.md imports Cookie from tough-cookie even though no exported symbol uses it.

scripts/api-extractor/run.ts could prune import lines whose binding appears nowhere else in the report.

[janbuchar]

The only risk here is that we may trigger a false alarm, right? Imports in the public API snapshot don't mean anything as far as backwards compatibility is concerned.