Consider note discovery batched requests

[nventuro]

Initially most requests will be one-off (check if note exists, if nullifier exists, etc.), except for fetchLogsByIndex (#9268), which will natively support batching to avoid multiple database scans.

It'll eventually make sense to accumulate requests and make larger batched requests (e.g. check multiple notes at once), but it's unclear how simple that'll be to do from inside Noir (once we swtich from the TS implementation).