Improve performance of "process_model_inferred_primary_keys"

[gshank]

Description

The method "process_model_inferred_primary_keys" method that was added by Add primary_key to manifest by dave-connors-3 · Pull Request #10096 · dbt-labs/dbt-core does not process only models that have been changed, but every single model in the manifest, which is not how it ought to work.

There may be other issues with gathering the generic tests to infer the primary key, but that's at the top of the list.