v0.2.1 — page-load spans carry the person

Fix: the spans from a page's first moments now carry the person.

0.2.0 held the first batch of spans until identity resolved, which was necessary and not sufficient. The underlying OpenTelemetry web SDK copies global attributes onto a span when the span starts, so documentLoad, documentFetch, resourceFetch and webvitals — all of which start before any session request can have answered — went out anonymous no matter how long their batch waited. Verified on a deployed app, which is the only place it shows.

The exporter now fills identity in as the batch leaves, for keys a span is missing. A span that started after a later identifyUser keeps the person it was created under.

No API change. Upgrading from 0.2.0 is a version bump.