Combine proptests and transcripts to perform top-level integration tests

[teor2345]

Is your feature request related to a problem? Please describe.

In #918, we wanted to move the block time check tests to zebra-consensus, but they depend on zebra-chain::generate.

• detailed explanation:
  • is_time_valid_at is also used in test code, specifically chain/src/block/tests/vectors.rs.
  • These tests should be moved into the consensus crate.
  • Some of the tests can't be moved, because they rely on the generate code, which isn't exposed to the rest of the crate API

Describe the solution you'd like

• The generate code should be expressed as proptest strategies (Rewrite block::tests::generate as proptest strategies. #919) to fix this.
• Then consensus tests can be written using the proptest strategies.
• In fact, rather than writing unit tests, we could combine proptests with the transcript functionality to perform top-level integration tests.
• Doing this correctly requires some amount of work but will save a lot of work compared to writing individual unit tests.

Post-implementation cleanup

• Inline zebra_chain::block::Header::is_time_valid_at into zebra_consensus::block::check::is_time_valid_at
• Make zebra_chain::block::header::BlockTimeError::InvalidBlockTime the source of zebra_consensus::error::BlockError::Time

My intuition is that we might not want to inline this, and instead take the first error message defined here, "invalid time in block header" and make that the error message on the variant in BlockError. Then we make BlockTimeError #[source] for BlockError::Time and have it only print "must be less than 2 hours in the future {0:?}" as its error message. This way we can let the reporter split the msg into multiple lines if it wants to which will make our error reports nicer imo.

Originally posted by @yaahc in #1146 (comment)

Describe alternatives you've considered

Keep the current implementation, which generates blocks without using proptests.

Additional context

This issue is blocked on #919

[teor2345]

Removing the volunteer tags from this issue, until it is unblocked.

[teor2345]

This is a good idea, but the tests are mostly ok. It might also be obsolete.