fix(note-transport): explicit block hint on sendPrivate; add sendPrivateOutput (0.16/next)

[WiktorStarczewski]

Summary

The 0.16 / next-channel version of #263 (which targets main/0.15). This is a breaking change, so it belongs on the next dist-tag.

Addresses maintainer review feedback (igamigo) on the private-note block-hint fix:

• client.notes.sendPrivate({ note, to }) now requires an explicit scanAfterBlockNum — the block the recipient scans forward from for the note's on-chain commitment — instead of the SDK inferring it from the client's current sync height. A hint above the commitment is never scanned back to, so the sync-height inference silently dropped delivery once the sender had synced past the note (e.g. relaying after waiting for the transaction to commit).
• New client.notes.sendPrivateOutput({ noteId, to }) derives the block from the output note's stored expected_height (the chain tip when its transaction was submitted) — exactly the value the review pointed to for output notes — so relaying one of this client's own notes is correct regardless of sync/relay timing.

The old sync-height auto-read is removed, so an arbitrary note is never silently relayed with a bad hint.

react-sdk's useTransaction / useSend / useMultiSend relay via sendPrivateOutputNote. Cross-client node regression tests guard both paths: the convenience method (delivers after the sender syncs past the commitment) and the agnostic sendPrivateNote (a deliberately-too-high explicit hint drops delivery). Verified compiling and passing against next's 0.16 miden-client.

Supersedes #263 (which targets main) for the 0.16 line.

closes #262

[igamigo]

LGTM! Just in case: we can still fix this in main by keeping the old signature (and adding a new function that adds the parameter). This will make the fix non-breaking and users (such as the wallet) can hotfix this by calling the new signature instead of the new one. If you think this is unnecessary though, please disregard!