chore(node/actor): Test: Empty Attributes while building unsealed payload

[pcw109550]

Adds one unit test which checks No attributes available but building unsealed payload triggered, leading critical error.

Moved test_builder helper to actor for reusability.

Part of #3070

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.9%. Comparing base (5faf212) to head (f06d2e5).
✅ All tests successful. No failed tests found.

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[op-will]

Looks good! You could merge as-is, but how do you feel about updating the test to handle all possible prepare_payload_attributes errors?

[op-will]

While we can rely on the default error returned from the default TestAttributesBuilder, that may change, causing this test to break. It may be better to:

1. Define different error types for TestAttributesBuilderError (Temporary, Critical, Reset) -- or even better, remove that error type and just use PipelineErrorKind
2. Update TestAttributesBuilder.prepare_payload_attributes to return the PipelineErrorKind of the configured error
3. Create and use a TestAttributesBuilder, add the exact error you want to receive to the attributes field
4. Assert that the error exactly matches the returned error

[op-will]

This also lets you parameterize this test to verify all error types (example) are handled how you expect them to be handled in a single test.

[op-will]

How do you feel about creating an actor_test.rs file and moving these tests/utils to it?

There are many branches in this logic, so there will eventually be many lines of unit tests, so we can de-clutter the live logic by moving to a separate file.

[theochap]

The way I'd go about it would be to have a test folder which is feature gated with #[cfg(test)] and put all the tests there

[op-will]

We're really testing the handling of prepare_payload_attributes errors.

Suggested change

	async fn test_build_unsealed_payload_no_attributes() {
	async fn test_build_unsealed_payload_prepare_payload_attributes_error() {

[op-will]

I think we would want to move this to a test_util.rs file since it's used in multiple files, but it is being removed soon: #3152

Although even without the builder, we'll still probably have some utils around creating the test SequencerActor.