Override the root span name

[barrettpyke]

Description

Currently the root span name is hard coded to OpenCode: ${getProjectName(input.worktree)}.

braintrust-opencode-plugin/src/tracing.ts

Line 284 in 1abb06e

name: `OpenCode: ${getProjectName(input.worktree)}`,

It would be nice to be able to override that name with a config value like rootSpanName. For context you can do this in the SDKs in functions like wrapTraced for instance (defaults to the function name).
https://www.braintrust.dev/docs/reference/sdks/typescript/3.7.0/typescript#param-args-name-3