upgrade sqlx to 0.8, add bdk_wallet and bdk_electrum

The new dependencies are part of the bdk upgrade and
include the improved wallet code.
They, too, depend on sqlite3.
However, they use a newer version than we currently use via sqlx.
This necessitated the sqlx upgrade.
This entailed trivial changes (use Pool directly instead of pool.acquire()).
We might have to fix the CI as well, I kept getting compile
errors from the macro until I ran swap/sqlx_dev_setup.sh.

Author: Einliterflasche