`basic-authorship`: debug level is now less spammy (#6768)

The `debug` level in `sc-basic-authorship` is now less spammy.
Previously it was outputing logs per individual transactions. It was
quite hard to follow the logs (and also generates unneeded traffic in
grafana).

Now `debug` level only show some internal details, without spamming
output with per-transaction logs. They were moved to `trace` level.

I also added the `EndProposingReason` to the summary INFO message. This
allows us to know what was the block limit (which is very useful for
debugging).

Example:
```
🎁

 Prepared block for proposing at 64 (1186 ms) hash: 0x4b5386c13c507d0dbab319ac054cc1bcfa08311e184452221ad07f12ecc6091c; parent_hash: 0x157c…ca5e; end: HitBlockWeightLimit; extrinsics_count: 7032; 
```

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Co-authored-by: GitHub Action <[email protected]>