Use Floresta as a replacement for mempool.space

[m1sterc001guy]

In some spots of our app, we need to query mempool.space for blockchain information. It would be interesting if we could replace that with UTreeXO based implementation floresta.

https://github.com/vinteumorg/Floresta

[m1sterc001guy]

Discussed this a bit today on a call. I think it makes the most sense to upstream our implementation of querying esplora for # of transactions, in which case ecash app wouldn't have any dependency on esplora.

The fedimint client would though, and I think it is worth investigating if Floresta could be used inside Fedimint directly.