feat(NTL): support attachments

[igamigo]

Also includes some minor refactors.
Closes #2286

• NTL-delivered notes with on-chain attachments now fetch their attachment content from the node during import, making them consumable.
• State sync now applies fetched attachments to tracked notes regardless of note type.
• Fetched content is validated before acceptance: type/content variant must match, attachments must match the authenticated commitment, and missing advertised attachments return RpcError::InvalidResponse. Also left some TODOs for further validations (will open an issue about this)
• import_notes now ensures genesis is present up front, avoiding fresh-store BlockHeaderNotFound(0) failures.
• Note transport now reports the header-derived on-chain note ID, not the locally rejoined note ID with empty attachments.
• Replaced sync_notes_with_details() with sync_notes_with_content(..., NoteContentFetch), returning self-contained ResolvedSyncNotesBlocks. NoteContentFetch defines whether
• Added fetch policies: PublicDetailsAndAttachments for state sync and AttachmentsOnly for import.
• Replaced SyncedNoteDetails with SyncedNote and ResolvedNoteContent, making private synced note details unrepresentable.
• Added CommittedNote::has_attachments() and block_num().
• Renamed: NoteSyncBlock to SyncNotesBlock, InputNoteRecord::set_attachments to attachments_received. THe latter now skips unchanged writes and reports whether the record changed.
• Import paths now build the partial MMR once per batch instead of once per note.
• State sync no longer needs side tables or per-note ID joins because SyncedNote carries its content.
• Renamed check_expected_notes to sync_expected_notes.