feat(c/node): Make dora_next_event thread-safe

[SanjayUG]

Feat: Make dora_next_event Thread-Safe

Which issue does this PR close?

• Closes #540

Rationale for this change

This change allows multiple threads to safely call dora_next_event concurrently while maintaining existing safety guarantees. The updates ensure that the DoraContext fields are accessed in a thread-safe manner.

What changes are included in this PR?

• feat(c/node): Make dora_next_event thread-safe
  • Wrap DoraContext fields in Arc<Mutex<>> for thread-safe access
  • Update dora_next_event to use shared references and mutex locking
  • Add comprehensive thread-safety documentation
  • Make dora_send_output thread-safe
  • Add proper error handling for mutex lock failures

Are these changes tested?

Yes, the changes have been tested to ensure that dora_next_event and dora_send_output can be called safely from multiple threads without causing race conditions or deadlocks.

Are there any user-facing changes?

No, there are no user-facing changes as this update is related to internal thread-safety improvements.

Are there any breaking changes to public APIs?

No, there are no breaking changes to public APIs.