Listenbrainz scrobbling (#1424)

* Refactor session_keys to its own package

* Adjust play_tracker

- Don't send external NowPlaying/Scrobble for tracks with unknown artist
- Continue to the next agent on error

* Implement ListenBrainz Agent and Auth Router

* Implement frontend for ListenBrainz linking

* Update listenBrainzRequest

- Don't marshal Player to json
- Rename Track to Title

* Return ErrRetryLater on ListenBrainz server errors

* Add tests for listenBrainzAgent

* Add tests for ListenBrainz Client

* Adjust ListenBrainzTokenDialog to handle errors better

* Refactor listenbrainz.formatListen and listenBrainzRequest structs

* Refactor agent auth_routers

* Refactor session_keys to agents package

* Add test for listenBrainzResponse

* Add tests for ListenBrainz auth_router

* Update ListenBrainzTokenDialog and auth_router

* Adjust player scrobble toggle

core/agents/session_keys_test.go

@@ -0,0 +1,37 @@
+package agents
+
+import (
+	"context"
+
+	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/tests"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("SessionKeys", func() {
+	ctx := context.Background()
+	user := model.User{ID: "u-1"}
+	ds := &tests.MockDataStore{MockedUserProps: &tests.MockedUserPropsRepo{}}
+	sk := SessionKeys{DataStore: ds, KeyName: "fakeSessionKey"}
+
+	It("uses the assigned key name", func() {
+		Expect(sk.KeyName).To(Equal("fakeSessionKey"))
+	})
+	It("stores a value in the DB", func() {
+		Expect(sk.Put(ctx, user.ID, "test-stored-value")).To(BeNil())
+	})
+	It("fetches the stored value", func() {
+		value, err := sk.Get(ctx, user.ID)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(value).To(Equal("test-stored-value"))
+	})
+	It("deletes the stored value", func() {
+		Expect(sk.Delete(ctx, user.ID)).To(BeNil())
+	})
+	It("handles a not found value", func() {
+		_, err := sk.Get(ctx, "u-2")
+		Expect(err).To(MatchError(model.ErrNotFound))
+	})
+})