Python/CPP should return scan results with per bucket grouping as in Rust client

[fresh-borzoni]

Search before asking

• I searched in the issues and found nothing similar.

Description

as per title,
what is now:

• Rust — per bucket HashMap<TableBucket, Vec<ScanRecord>>
• Python — flat List[ScanRecord], each carries bucket
• CPP — flat Vec<FfiScanRecord>, each carries bucket_id

Willingness to contribute

• I'm willing to submit a PR!