fix: Add additional timeout for mappers

[fuzzybinary]

What and why?

We're getting reports that event mappers still time out, even with 1s of available time. This is likely because of a sudden influx of calls on the method channel, which is hopefully temporary and can be resolved within the new timeout (5s).

Additionally, we're seeing reports of notImplemented errors when calling mappers. This appears to be caused by users or third party libraries creating multiple Flutter engines (some of which don't initialize Datadog) or some weird (and very difficult to reproduce cases) where it appears that Flutter does not unregister the plugin. To fix this, we'll attempt to call other mappers if the first one returns NotImplemented, and remove the offending method channel from the list.

Add formerly missing mapper "not implemented" telemetry to iOS.

Add an integration test for user information.

refs: RUM-6457 #652

Review checklist

• [ ] This pull request has appropriate unit and / or integration tests
• [x] This pull request references a Github or JIRA issue