Release v6.63.0

What's Changed

• feat(pnr): harden: publishes a hard-macro abstract (#95 step 1) by @hernloh in #674
• feat(pnr,synth): blocks: consumes hardened abstracts (#95 step 2) by @hernloh in #675
• feat(pnr,synth): refuse stale block abstracts; --accept-stale (#95 step 3) by @hernloh in #676

Full Changelog: v6.62.0...v6.63.0