Bun runtime support

[keturiosakys]

Goal

Support feature-parity for client library and Studio for apps running on the Bun runtime

Main identified issues:

• Fetch requests result in brand new traces, instead of associating to a parent Hono Request span
• Proxied requests lose all headers. fixed

[brettimus]

i want to update a bit about why this is open: when i played with bun on test repos, i ended up with a lot of rogue spans, and never had time to debug why

it seems the otel client library does produce some accurate spans, but also a lot of noise. anyone who is interested on fleshing out a bug report is welcome to chime in :)