* pre-checking: Reject failed PVFs

* paras: immediately reject any PVF that cannot reach a supermajority

* Make the `quorum` reject condition a bit more clear semantically

* Add comment

* Update implementer's guide

* Update a link

Not related to the rest of the PR, but I randomly noticed and fixed this.

* Update runtime/parachains/src/paras/tests.rs

Co-authored-by: s0me0ne-unkn0wn <[email protected]>

* Remove unneeded loop

* Log PVF retries using `info!`

* Change retry logs to `warn!` and add preparation failure log

* Log PVF execution failure

* Clarify why we reject failed PVFs

* Fix PVF reject runtime benchmarks

Co-authored-by: s0me0ne-unkn0wn <[email protected]>