Replace old used-to-be-GORM datastructures (#104305) with sqlc-generated
structs. This also makes it possible to use more specific structs that
are more taylored to the specific queries, increasing efficiency.
This commit mostly deals with workers, including the sleep schedule and
task scheduler.
Functional changes are kept to a minimum, as the API still serves the
same data.
Because this work covers so much of Flamenco's code, it's been split up
into different commits. Each commit brings Flamenco to a state where it
compiles and unit tests pass. Only the result of the final commit has
actually been tested properly.
Ref: #104343
Avoid users of the persistence layer to have to test against Gorm errors,
by wrapping job/task errors in a new `PersistenceError` struct.
Instead of testing for `gorm.ErrRecordNotFound`, code can now test for
`persistence.ErrJobNotFound` or `persistence.ErrTaskNotFound`.
