RFC: method signature improvement proposal for `blockchain.silentpayments.subscribe`

[Overtorment]

We are internally working on own electrum server with SP capabilities, and thinking about adopting Frigate's proposed method blockchain.silentpayments.subscribe.
After discussing internally with @limpbrains, a couple of additions would make dev life a bit easies:

• method blockchain.silentpayments.subscribe should also accept optional end param which should tell server to stop scanning when its reached. This should enable (mostly for dev purposes) usecases like "please rescan specific day only"
• notifications should also return progress_height, so in case of losing connection/switching to a new server client can subscribe from that height

[craigraw]

Apologies for the slow response, and thanks for the suggestions.

The first suggestion has been implemented in the protocol - the start parameter also accepts a string in the form "FROM-TO".

As to the second suggestion, I believe it's too restrictive. Because silent payments scanning can be done in any order (and sharing a batched workload may result in performance benefits) I think adding this requirement to the protocol will slow some implementations down - certainly it will in Frigate's case, which does batching on the GPU.

[Overtorment]

ah batching is a perfect explanation why progress_height might not work.

for now, if we want to query several servers at the same time probably the best way to distribute load is to use already implemented start and end