chore: Added helper to reduce code duplication between Db.propose and Proposal.create_proposal

[bernard-avalabs]

Addresses #1342.

Created a propose_with_parent to allow code reuse between Db.propose and Proposal.create_proposal. propose_with_parent will also choose between using parallel or serial proposal creation based on the batch size. Currently the batch size for using parallel creation is 8, but there is a TODO to update the constant once we have some experimental results. We use size_hint() on the batch iterator to estimate the batch size.

[rkuris]

Looks good, but please apply the comments before merging.

[rkuris]

Great start, but I think we can do a bit better, especially since this area is likely to change.

IMO the right way to fix this is to use a value set at database open time as the value of force_parallel. This is because I think we'll eventually need some way to mark parallel as always disabled.

IMO the best way to fix this is to create an enum with values NEVER, BATCH_SIZE(usize), ALWAYS set at database open time. That has the higest readability and would probably make this code change much cleaner.

[bernard-avalabs]

IMO the right way to fix this is to use a value set at database open time as the value of force_parallel. This is because I think we'll eventually need some way to mark parallel as always disabled.

IMO the best way to fix this is to create an enum with values NEVER, BATCH_SIZE(usize), ALWAYS set at database open time. That has the higest readability and would probably make this code change much cleaner.

I don't think we need both a force_parallel Option and an enum. I've instead added a enum field in Db, and set BatchSize (8 currently) as the default configuration value. Instead of checking for an option, it performs a match on an Enum during proposal creation. Please let me know if I've misunderstood your comment.