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.

cmd/gen/sqlc-wrapper/main.go

@@ -449,18 +449,18 @@ func buildBody(m methodInfo) string {
 
 	// no repo-typed result → direct return
 	if len(m.Results) == 0 || m.Results[0].RepoType == "" {
-		return "\treturn " + call + "\n"
+		return "\treturn mapErr(" + call + ")\n"
 	}
 
 	r := m.Results[0]
 	if r.IsSlice {
 		return fmt.Sprintf(
-			"\trows, err := %s\n\tif err != nil {\n\t\treturn nil, err\n\t}\n\tout := make([]%s, len(rows))\n\tfor i, row := range rows {\n\t\tout[i] = %s(row)\n\t}\n\treturn out, nil\n",
+			"\trows, err := %s\n\tif err != nil {\n\t\treturn nil, mapErr(err)\n\t}\n\tout := make([]%s, len(rows))\n\tfor i, row := range rows {\n\t\tout[i] = %s(row)\n\t}\n\treturn out, nil\n",
 			call, r.RepoType, converterFn(r.TypeStr),
 		)
 	}
 	return fmt.Sprintf(
-		"\tr, err := %s\n\tif err != nil {\n\t\treturn %s{}, err\n\t}\n\treturn %s(r), nil\n",
+		"\tr, err := %s\n\tif err != nil {\n\t\treturn %s{}, mapErr(err)\n\t}\n\treturn %s(r), nil\n",
 		call, r.RepoType, converterFn(r.TypeStr),
 	)
 }
@@ -477,6 +477,8 @@ package {{.PkgName}}
 
 import (
 	"context"
+	"database/sql"
+	"errors"
 
 	"{{.RepoPkg}}"
 )
@@ -491,6 +493,22 @@ func NewStore(q *Queries) repository.Store {
 	return &Store{q: q}
 }
 
+var errMap = []struct {
+	from error
+	to   error
+}{
+	{sql.ErrNoRows, repository.ErrNotFound},
+}
+
+func mapErr(err error) error {
+	for _, e := range errMap {
+		if errors.Is(err, e.from) {
+			return e.to
+		}
+	}
+	return err
+}
+
 {{range .ModelTypes -}}
 func {{converterFn .}}(v {{.}}) repository.{{.}} {
 	return repository.{{.}}(v)