Implement `Deref<Target=Client>` for `ElectrumBlockchain`

[afilini]

Description

As pointed out in https://github.com/bitcoindevkit/rust-electrum-client/pull/58#issuecomment-1207890096 there was no way to keep using the client once it was given to BDK.

Checklists

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[tnull]

Thank you for having a look at this! Could you also add the same for EsploraClient?

[vladimirfomene]

@afilini #722 implements this for our Esplora clients. I just created it in case this is needed urgently. This will change a bit once we refactor our Esplorablockchain code to incoroporate our new rust-esplora-client

[tnull]

@afilini #720 implements this for our Esplora clients. I just created it in case this is needed urgently. This will change a bit once we refactor our Esplorablockchain code to incoroporate our new rust-esplora-client

Thanks for having a look a this! @afilini also created a BDK branch that makes use of the updated external rust-esplora-client (https://github.com/afilini/bdk/tree/feat/use-external-esplora-client), which implements this. I'm currently tracking this branch for my development.