Motivation

When a network resource fails (timeout, no connectivity), the SDK emits a 'RUMErrorEvent'
Currently the error event schema has no trace context fields ('trace_id', 'span_id', 'parent_span_id', 'rule_psr')
and no 'graphql' struct on 'error.resource', unlike the success path ('RUMResourceEvent') which already has both.

This means cross-platform SDKs (React Native, Flutter) silently lose trace and GraphQL attributes on the error path.

Changes

• Added trace context fields ('trace_id', 'span_id', 'parent_span_id', 'rule_psr') to '_dd' in the error event schema, mirroring 'RUMResourceEvent._dd'
• Added 'graphql' struct to 'error.resource', mirroring 'RUMResourceEvent.resource.graphql'
• Added 'error-schema.json' to the casing exceptions in 'scripts/validate.mjs' (same as 'resource-schema.json', since GraphQL field names follow camelCase convention)