syz-cluster: prioritize blob-based base commits

Consider Cc'd mailing lists when selecting the exact base commit.

Among the base commits determined based on blob sha value from the git
patch, first select the ones that match both the trees of the Cc'd
subsystems and their primary branches.

If it gives no exact match, select a base commit that comes from a tree
of a Cc'd subsystem. As fallback, take any subsystem tree.

This should prevent valid, but suprising patch series triage results.

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