test(app): improve context cancellation handling in submission flow

[sachin9058]

Type of change

• Improvement (improvement to code, performance, etc)
• Test update

Description

This PR improves consistency of context cancellation handling across transaction submission flows.

Changes include:

• Added early context checks at the start of SubmitTransaction and SubmitTransactionWithWait

• Ensured retry loop exits promptly when context is canceled

• Added test coverage for:

  • cancellation before submission
  • cancellation before notification flow
  • cancellation during retry execution

These changes improve correctness and predictability without modifying existing behavior or APIs.

Additional details (Optional)

• No changes to retry logic or public interfaces
• All tests pass locally (go test ./...)
• Linting and formatting checks pass (make lint)

Related issues

Closes #192

[sachin9058]

Hi @mbrandenburger,

I’ve opened this PR as a small follow-up improvement focused on context cancellation handling. It’s intentionally minimal and test-focused, without changing existing behavior.

Whenever you have time, I’d really appreciate your feedback. Happy to make any adjustments if needed.