electrs: adapt to version 0.9.0

- `waitfornewblock` was previously not included in the public RPC
  whitelist because it's reserved for testing and marked as hidden
  in bitcoind.

- electrs changed its verbosity settings. `-vv` is now the best choice
  for normal usage.

- bitcoind option `dataDirReadableByGroup` is now unused.
  Because it can be valuable for other use cases and implementing
  it is intricate, we're keeping it for now.

- test: keep `nc` connection open because otherwise the electrs
  RPC server would now close the connection before sending a response.

examples/configuration.nix

@@ -93,10 +93,6 @@
   ### ELECTRS
   # Set this to enable electrs, an efficient Electrum server implemented in Rust.
   # services.electrs.enable = true;
-  #
-  # If you have more than 8GB memory, enable this option so electrs will
-  # sync faster. Only available if hardware wallets are disabled.
-  # services.electrs.high-memory = true;
 
   ### BTCPayServer
   # Set this to enable BTCPayServer, a self-hosted, open-source
@@ -150,7 +146,6 @@
   ### Hardware wallets
   # Enable the following to allow using hardware wallets.
   # See https://github.com/bitcoin-core/HWI for more information.
-  # Only available if electrs.high-memory is disabled.
   #
   # Ledger must be initialized through the official ledger live app and the Bitcoin app must
   # be installed and running on the device.
@@ -264,5 +259,5 @@
   # The nix-bitcoin release version that your config is compatible with.
   # When upgrading to a backwards-incompatible release, nix-bitcoin will display an
   # an error and provide hints for migrating your config to the new release.
-  nix-bitcoin.configVersion = "0.0.51";
+  nix-bitcoin.configVersion = "0.0.53";
 }