[xcm-emulator] Better logs for message execution and processing (#5712)

When running XCM emulated tests and seeing the logs with `RUST_LOG=xcm`
or `RUST_LOG=xcm=trace`, it's sometimes a bit hard to figure out the
chain where the logs are coming from.

I added a log whenever `execute_with` is called, to know the chain which
makes the following logs. Looks like so:

<img width="1499" alt="Screenshot 2024-09-13 at 20 14 13"
src="https://github.com/user-attachments/assets/a31d7aa4-11d1-4d3e-9a65-86f38347c880">

There are already log targets for when UMP, DMP and HRMP messages are
being processed. To see them, you have to use the log targets `ump`,
`dmp`, and `hrmp` respectively. So `RUST_LOG=xcm,ump,dmp,hrmp` would let
you see every log.
I prefixed the targets with `xcm::` so you can get all the relevant logs
just by filtering by `xcm`. You can always use the whole target to see
just the messages being processed.

These logs showed the message as an array of bytes, I made them show a
hexadecimal string instead since that's easier to copy in case you want
to decode it or use it in another tool. They look like this now:

<img width="1499" alt="Screenshot 2024-09-13 at 20 17 15"
src="https://github.com/user-attachments/assets/5abf4a97-1ea7-4832-b3b0-d54c54905d1a">

The HRMP and UMP ones are very similar.