Further optimize sbom/license metadata generation

This takes a clean `m nothing` for `cheetah-trunk_staging-userdebug`
build on my machine from 9m39s to 5m58s (average of 2 runs each).

The actual ckati run stats:
 * Wall time: 6m47s -> 3m17s
 * MaxRSS: 23627MB -> 23905MB

Bug: 406475346
Test: treehugger
Test: manual performance comparisons
Test: ninja files are identical
Change-Id: I50eaab9622df391ee6ff7eea43f8e79a1055e1ec