[Feature] Speed up consensus version unit testing

[vicsn]

🚀 Feature

There is a lot to improve on our compilation and testing front. One specific concern is that developers should feel comfortable writing new integration unit tests, such as the once in test_v*.rs.

Taking an example for running some tests in test_v9:

• a build from scratch takes multiple minutes. A trivial incremental build takes 1-1.5 minutes. Setting lto=off in the test profile would degrade CI performance. Should we create a custom test profile for CI with lto=thin? I tried setting RUSTFLAGS="-C lto=off" to override the profile but that gives me a linker error.
• individual tests take 30-120 seconds. The biggest reason for this is block and proof generation.
  • Can we locally cache ledgers up to the appropriate starting height after the first run of the unit test?
  • We can consider turning off proof verification and relying on evaluation instead of execution, and assume that there is a set of tests which checks for equivalence of evaluation and execution.