[OTel]: Internal span model throws away half of OTel attrs #169

When telemetry comes in we flatten it into a little internal Span with no status, kind, resource, scope, events, or links.

So span status is never read anywhere, so an errored LLM/tool span with no error.type scores as a success, and resource attrs get dropped or merged backwards. Bigger piece of work, but it's the root cause under a lot of the other OTel issues.

Direction: make the OTLP data model the internal model, and read span status as the primary failure signal.