test(plugins): speed up integration tests (~45% improvement) (#5137)

* test(plugins): speed up integration tests with shared wazero cache

Reduce plugin test suite runtime from ~22s to ~12s by:

- Creating a shared wazero compilation cache directory in TestPlugins()
  and setting conf.Server.CacheFolder globally so all test Manager
  instances reuse compiled WASM binaries from disk cache
- Moving 6 createTestManager* calls from inside It blocks to BeforeAll
  blocks in scrobbler_adapter_test.go and manager_call_test.go
- Replacing time.Sleep(2s) in KVStore TTL test with Eventually polling
- Reducing WebSocket callback sleeps from 100ms to 10ms

Signed-off-by: Deluan <deluan@navidrome.org>

* test(plugins): enhance websocket tests by storing server messages for verification

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

plugins/host_users_test.go

@@ -486,7 +486,6 @@ func setupTestUsersConfig(tmpDir string) {
 	conf.Server.Plugins.Enabled = true
 	conf.Server.Plugins.Folder = tmpDir
 	conf.Server.Plugins.AutoReload = false
-	conf.Server.CacheFolder = filepath.Join(tmpDir, "cache")
 }
 
 // testUsersInput represents input for test-users plugin calls