Bug: `/otel/v1/traces` does not decompress gzip

[nizmle]

Identical OTLP/JSON payload, same headers. Uncompressed → 200. Gzipped → 400.

curl -X POST https://api.braintrust.dev/otel/v1/traces \
  -H "Authorization: Bearer $KEY" -H "x-bt-parent: project_id:$PROJECT" \
  -H "Content-Type: application/json" --data-binary @payload.json          # 200

gzip -c payload.json > payload.json.gz
curl -X POST https://api.braintrust.dev/otel/v1/traces \
  -H "Authorization: Bearer $KEY" -H "x-bt-parent: project_id:$PROJECT" \
  -H "Content-Type: application/json" -H "Content-Encoding: gzip" \
  --data-binary @payload.json.gz                                           # 400

The gzipped request returns Invalid traces data: resourceSpans Required, i.e. the compressed bytes
are parsed as JSON without inflating first.

This blocks Cloudflare Workers Observability entirely. Cloudflare always sends Content-Type: application/json with Content-Encoding: gzip , confirmed by echoing the request to our own Worker and logging the first bytes as 1f 8b 08 00.

There is no setting on either side to turn it off. gzip is standard in the OTLP/HTTP spec.