Retry failed PVF execution (AmbiguousWorkerDeath) (#6235)

* Fix a couple of typos

* Retry failed PVF execution

PVF execution that fails due to AmbiguousWorkerDeath should be retried once.
This should reduce the occurrence of failures due to transient conditions.

Closes #6195

* Address a couple of nits

* Write tests; refactor (add `validate_candidate_with_retry`)

* Update node/core/candidate-validation/src/lib.rs

Co-authored-by: Andronik <[email protected]>

Co-authored-by: eskimor <[email protected]>
Co-authored-by: Andronik <[email protected]>