## Problem
`TestMigrate/Parallel` flakes with:
```
timeout: can't acquire database lock
```
## Root Cause
The test runs two concurrent `migrations.Up(db)` calls on the same
database. golang-migrate wraps every `Lock()` call with a [15-second
timeout](https://github.com/golang-migrate/migrate/blob/v4.19.0/migrate.go#L29)
(`DefaultLockTimeout`). Our `pgTxnDriver.Lock()` uses
`pg_advisory_xact_lock`, which blocks until the lock is available. With
430+ migrations, the first caller can hold the lock well beyond 15s (the
failing test ran for 25.88s), causing the second caller to hit the
timeout.
## Fix
Set `m.LockTimeout = 2 * time.Minute` after creating the
`migrate.Migrate` instance in `setup()`. Since `pg_advisory_xact_lock`
releases automatically when the transaction commits, there's no risk of
a stuck lock — we just need to wait long enough for a concurrent
migration to finish.
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.
Updates coder/customers#365
This PR updates our migration framework to run all migrations in a single transaction. This is the same behavior we had in v1 and ensures that failed migrations don't bring the whole deployment down. If a migration fails now, it will automatically be rolled back to the previous version, allowing the deployment to continue functioning.
Kyle Carberry