GraphQL diagnostics_channel tracing publishes non-structured-cloneable payloads in Cloudflare Workers Tail Workers

GraphQL.js 17 resolves `node:diagnostics_channel` at module load and creates `graphql:*` tracing channels.

In Cloudflare Workers with `nodejs_compat` and a Tail Worker attached, Cloudflare forwards diagnostics channel messages to Tail Workers as `diagnosticsChannelEvents`. That forwarding appears to require structured-cloneable payloads.

GraphQL diagnostic contexts include objects like `GraphQLSchema`, `DocumentNode`, `Source`, execution results, resolver args/results, etc. Some of these are not structured-cloneable. In production this causes Cloudflare runtime log errors like:

`Failed to publish diagnostics channel message:`

The request itself still succeeds; logs get polluted with runtime errors.

### Reproduction shape

1. Deploy a Cloudflare Worker with:
- `compatibility_flags = ["nodejs_compat"]`
- a Tail Worker configured
- GraphQL.js 17
2. Execute a GraphQL request through GraphQL Yoga or direct GraphQL.js parse/validate/execute.
3. Runtime logs repeatedly show:

`Failed to publish diagnostics channel message:`

This happens even without application-level OpenTelemetry.

### Relevant GraphQL.js behavior

`graphql/diagnostics.mjs` does:

```js
const dc = resolveDiagnosticsChannel();
export const parseChannel = dc?.tracingChannel('graphql:parse');
export const validateChannel = dc?.tracingChannel('graphql:validate');

and emission sites trace when channel.hasSubscribers is true.

On Cloudflare, Tail forwarding appears to act as a diagnostics subscriber, so tracing is enabled even when the app did not intentionally subscribe to GraphQL diagnostics.

### Expected behavior

GraphQL.js 17 should work in Cloudflare Workers with Tail Workers enabled without runtime diagnostics errors.

Possible fixes:

- expose an official opt-out for GraphQL diagnostics tracing,
- avoid publishing non-structured-cloneable objects by default,
- provide serialization/sanitization hooks,
- or avoid enabling tracing for infrastructure-level diagnostics forwarding.

### Workaround

We patched resolveDiagnosticsChannel() to return undefined, disabling GraphQL diagnostics entirely. That works, but it is brittle and disables useful instrumentation.

Start with graphql/diagnostics.mjs and resolveDiagnosticsChannel(), then reproduce the listed Cloudflare Worker setup with nodejs_compat, a Tail Worker, and a GraphQL parse/validate/execute request. Compare the tracing emission sites and the proposed opt-out, sanitization, and serialization approaches; done means GraphQL.js works without Cloudflare runtime diagnostics errors while useful instrumentation remains possible.

Written by the indexing model from the issue text.