Investigate poor validation performance.

[lemmih]

Issue summary

Some tipsets around epoch 3141096 are slow to validate (10s to 30s on my rather powerful machine). This is quite a bit slower than the usual 1s-2s for most other tipsets. Investigate why these tipsets are slow to validate and determine if there's anything we can improve in Forest.

Tasks:

• [ ] Reproduce the problem with a snapshot for epoch 3141096.
• [ ] Investigate what is causing the slow-down.
• [ ] Determine whether there's anything to improve in Forest or if the problem lies entirely in the FVM.

Other information and links

DO link to snapshot: https://forest-snapshots.fra1.cdn.digitaloceanspaces.com/debug/#3551/forest_snapshot_mainnet_2023-08-20_height_3141096.forest.car.zst