Implement Anchor for BlockId

[vladimirfomene]

Description

This PR fixes #1062.
It implements the Anchor trait on BlockId.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

[notmandatory]

Is it possible to demonstrate using this in a test or example?

[vladimirfomene]

@notmandatory let me look into it.

[evanlinjin]

Thanks for this! Just some thoughts.

[vladimirfomene]

I think I will be using this for the Nakamoto syncing logic, @evanlinjin do you have an idea on how to write an example or test for this?

[evanlinjin]

I think I will be using this for the Nakamoto syncing logic, @evanlinjin do you have an idea on how to write an example or test for this?

I think a documentation test for Anchor will be nice.

Like using a LocalChain with a single block, creating multiple TxGraphs with different anchor types and anchoring a single tx into the TxGraphs with the different anchor types.

[evanlinjin]

And did tokio just break our MSRV?

[vladimirfomene]

Will rebase once #1077 gets merged

[danielabrozzoni]

Just a couple of nits :)

[evanlinjin]

Good work, we are nearly there. Documentation can be better.

[evanlinjin]

ACK 18e8da3