Investigate 8.5 regressions

# Regressions

1. Block context acquisition (issue of `TVar` contention?) regression needs to resolved - note the absolute value of the regression is the same for both the value and the plutus workloads. Regression present since `8.2.1`.
2. Mempool snapshotting regression needs to be resolved - note that the absolute value is significantly different between the value and Plutus workload. after `8.2.1`.

Value only workload metrics:


# Versions to compare

See manifests for details.

- For regression 1: [8.1.2](https://github.com/input-output-hk/ouroboros-consensus/files/13165946/manifest.8.1.2.d2d90b48c.json) vs [8.2.1](https://github.com/input-output-hk/ouroboros-consensus/files/13165950/manifest.8.2.1-pre.a29ee68ba.json)
- For regression 2: [8.2.1](https://github.com/input-output-hk/ouroboros-consensus/files/13165950/manifest.8.2.1-pre.a29ee68ba.json) vs [8.5.0](https://github.com/input-output-hk/ouroboros-consensus/files/13165952/manifest.8.5.0-pre.f1ce77083.json)

# Subtasks

- [ ] https://github.com/IntersectMBO/ouroboros-consensus/issues/465