Riverqueue

Changed

- License changed from LGPLv3 to MPL-2.0.
- **DATABASE MIGRATION**: Database schema v3, alter river_job tags column to set a default of `[]` and add not null constraint.

Changed

- Constants renamed so that adjectives like `Default` and `Min` become suffixes instead of prefixes. So for example, `DefaultFetchCooldown` becomes `FetchCooldownDefault`.
- Rename `AttemptError.Num` to `AttemptError.Attempt` to better fit with the name of `JobRow.Attempt`.
- Document `JobState`, `AttemptError`, and all fields its fields.
- A `NULL` tags value read from a database job is left as `[]string(nil)` on `JobRow.Tags` rather than a zero-element slice of `[]string{}`. `append` and `len` both work on a `nil` slice, so this should be functionally identical.

Changed

- `JobRow`, `JobState`, and a other related types move into `river/rivertype` so they can more easily be shared amongst packages. Most of the River API doesn't change because `JobRow` is embedded on `river.Job`, which doesn't move.

Changed

- Remove `replace` directive from the project's `go.mod` so that it's possible to install River CLI with `latest`.

Changed

- Allow River clients to be created with a driver with `nil` database pool for use in testing.
- Update River test helpers API to use River drivers like `riverdriver/riverpgxv5` to make them agnostic to the third party database package in use.
- Document `Config.JobTimeout`'s default value.
- Functionally disable the `Reindexer` queue maintenance service. It'd previously only operated on currently unused indexes anyway, indexes probably do _not_ need to be rebuilt except under fairly rare circumstances, and it needs more work to make sure it's shored up against edge cases like indexes that fail to rebuild before a clien restart.

Changed

- Fix license detection issues with `riverdriver/riverpgxv5` submodule.
- Ensure that river requires the `riverpgxv5` module with the same version.