feat(db): add memory storage driver

removes the sqlite dependency for tests, also brings back the option for
users to run zero persistence instances of tinyauth.

adds new mapErr fn for sqlc wrapper gen to prevent sql errors from
leaking out of the store implementation.

internal/model/config.go

@@ -4,7 +4,8 @@ package model
 func NewDefaultConfiguration() *Config {
 	return &Config{
 		Database: DatabaseConfig{
-			Path: "./tinyauth.db",
+			Driver: "sqlite",
+			Path:   "./tinyauth.db",
 		},
 		Analytics: AnalyticsConfig{
 			Enabled: true,
@@ -82,7 +83,8 @@ type Config struct {
 }
 
 type DatabaseConfig struct {
-	Path string `description:"The path to the SQLite database, including file name." yaml:"path"`
+	Driver string `description:"The database driver to use. Valid values: sqlite, memory." yaml:"driver"`
+	Path   string `description:"The path to the SQLite database, including file name. Only used when driver is sqlite." yaml:"path"`
 }
 
 type AnalyticsConfig struct {