Caching pipeline_project outside of loop to avoid multple lookups

[hugabora]

Description

Scheduler checks in a loop whether a block is an integration block. This instantiates Project object in each call which is quite slow and adds considerably, esp. when many blocks are in the pipeline.

The change caches the pipeline project outside of the loop. The method now takes the cached object as an optional parameter and avoids lookups.

How Has This Been Tested?

Tested in my local project.

Checklist

• The PR is tagged with proper labels (bug, enhancement, feature, documentation)
• I have performed a self-review of my own code
• I have added unit tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

cc:
@wangxiaoyou1993