Migrate bincode

[shawn-zil]

https://rustsec.org/advisories/RUSTSEC-2025-0141
Switch back to bincode-1.3.3 as an interim measure. Migration is an expensive strategy.

Modules impacted:

1. Checkpoints: modify convert-ckpt to convert bincode-2 to bincode-1 formats; migrate to bincode-1.
2. Credits: migrate to bincode-1 before release v0.20.0 goes out.
3. Database: restore to bincode-1 as-is.
4. State: restore to bincode-1 as-is.