feat(metrics): Attribute integration-emitted metrics

[sentry-junior]

Allow registered integrations to identify metrics emitted through the shared metrics API. Integration metadata now reaches metric attributes and envelope headers, with mixed batches partitioned by SDK identity so manual metrics remain attributed to sentry.ruby.

Wire the Yabeda adapter as the first consumer so its metrics are reported as sentry.ruby.yabeda.

Linear: https://linear.app/getsentry/issue/RUBY-210/attribute-auto-emitted-metrics-to-integrations

Requested by johdax.

[linear-code]

RUBY-210

[sl0thentr0py]

The canonical way is to add the metrics methods with an attribute passthrough in
https://github.com/getsentry/sentry-ruby/blob/master/sentry-ruby/lib/sentry/integrable.rb

I can just take this over if you don't mind.

[sl0thentr0py]

sdk.name and sdk.version should only be filled in scope.apply_to_telemetry, don't fill them in in MetricEvent but hold an integration_meta reference there that should be picked up in scope.apply_to_telemetry

[sl0thentr0py]

telemetry_event_buffer new envelope doesn't actually need any headers except sent_at so remove all the other stuff and also revert the grouping