Decompose the monolithic internal/provider/telemost package into two
orthogonal layers: engine/goolom (Yandex proprietary SFU wire protocol —
WebSocket signaling, dual pub/sub PeerConnections, DataChannel, telemetry)
and auth/telemost (HTTP connection-info fetch → engine.Credentials).
Add engine.Config.Refresh callback so Goolom can obtain fresh peerID and
credentials on every reconnect without a direct dependency on the auth
package. engine_adapter wires the Refresh closure from authProvider.Issue.
Delete internal/provider/ entirely (telemost was the last tenant) and
remove the now-obsolete provider_adapter + its test from builtin.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
