[CT-1881] [Feature] When possible, bypass an expensive method during graph construction

[dbeatty10]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

#6073 describes how projects with 1000's of nodes can take ~15 minutes to dbt build even a single node.

The _already_known method call is a relatively expensive method call during DAG parsing. There are some cases where it is unnecessarily called, namely when in_degree != 0 here.

Swapping the conditions of the if statement would short-circuit calling _already_known while keeping the logic the same. This is shown in 9f96087. (We know we can safely swap the order by commutativity of conjunction).

Describe alternatives you've considered

There's at least two alternatives:

1. Default approach of changing nothing
2. More complicated refactor

This proposal seems obviously superior to the first alternative while not preventing us from taking up the second alternative at a later date. So it's an easy win.

Who will this benefit?

This will (slightly) benefit teams with very large DAGs (thousands of nodes).

Are you interested in contributing this feature?

There's already a PR ready for this!

Anything else?

No response

[jtcohen6]

Renamed the issue just to make clear that this is graph generation, not project parsing!