Implement logging

[luisschwab]

We currently don't log anything in this library. Emit tracing events on client building and requests which may be consumed by downstream users.

[EliteCoder18]

I’d like to work on this. I’m planning to add an optional, non-default log feature backed by tracing, following the approach discussed in bitcoindevkit/bdk#1995. Since this is a standalone crate, I would use local feature-gated logging macros instead of introducing the bdk_common crate. If that direction sounds good, could you assign this issue to me?