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/repository/memory/store.go

@@ -0,0 +1,27 @@
+// Package memory provides an in-memory implementation of repository.Store for use in tests.
+package memory
+
+import (
+	"sync"
+
+	"github.com/tinyauthapp/tinyauth/internal/repository"
+)
+
+// Store is a thread-safe in-memory implementation of repository.Store.
+type Store struct {
+	mu         sync.RWMutex
+	sessions   map[string]repository.Session
+	oidcCodes  map[string]repository.OidcCode
+	oidcTokens map[string]repository.OidcToken
+	oidcUsers  map[string]repository.OidcUserinfo
+}
+
+// New returns a new empty in-memory Store.
+func New() repository.Store {
+	return &Store{
+		sessions:   make(map[string]repository.Session),
+		oidcCodes:  make(map[string]repository.OidcCode),
+		oidcTokens: make(map[string]repository.OidcToken),
+		oidcUsers:  make(map[string]repository.OidcUserinfo),
+	}
+}