docs: 4.6.0 post must state the dev-tooling targets that were not met

The 4.6.0 release post's tests section must say plainly which dev-tooling targets were NOT met, with the measured numbers: shared-change land 255 s vs 120 s target; our tooling peaks at 8 cores vs the 4-core cap (not enforced yet, #632); warm bun run test still 11-13 s vs 10 s.

Working on this in #635 (draft). Branch fix/634-docs-4-6-0-post-must. Regression test first, then the fix.