This PR is the first in a series aimed at closing
[#15109](https://github.com/coder/coder/issues/15109).
### Changes
- **Template Database Creation:**
`dbtestutil.Open` now has the ability to create a template database if
none is provided via `DB_FROM`. The template database’s name is derived
from a hash of the migration files, ensuring that it can be reused
across tests and is automatically updated whenever migrations change.
- **Optimized Database Handling:**
Previously, `dbtestutil.Open` would spin up a new container for each
test when `DB_FROM` was unset. Now, it first checks for an active
PostgreSQL instance on `localhost:5432`. If none is found, it creates a
single container that remains available for subsequent tests,
eliminating repeated container startups.
These changes address the long individual test times (10+ seconds)
reported by some users, likely due to the time Docker took to start and
complete migrations.
Fixes the flake seen here: https://github.com/coder/coder/runs/25832852690
Linux is not a real time operating system, and so there is no guarantee that subsequent `time.Now()` `time.Since()` calls will return a non-zero time. This assert is mainly there to ensure we don't return `-1`.
fixes#11950https://github.com/coder/coder/issues/11950#issuecomment-1987756088 explains the bug
We were also calling into `Unlisten()` and `Close()` while holding the mutex. I don't believe that `Close()` depends on the notification loop being unblocked, but it's hard to be sure, and the safest thing to do is assume it could block.
So, I added a unit test that fakes out `pq.Listener` and sends a bunch of notifies every time we call into it to hopefully prevent regression where we hold the mutex while calling into these functions.
It also removes the use of a `context.Context` to stop the PubSub -- it must be explicitly `Closed()`. This simplifies a bunch of the logic, and is how we use the pubsub anyway.
Adds prometheus metrics to PGPubsub for monitoring its health and performance in production.
Related to #11950 --- additional diagnostics to help figure out what's happening
