fix(cardano-chain-follower): Refactor cardano-chain-follower to fix client concurrency bug

[FelipeRosa]

Description

This PR fixes a bug that caused the Follower to get stuck when trying to set its read pointer while waiting for the next chain update.

Related Issue(s)

Closes #180

Description of Changes

Background task

• Follower background task refactored to allow dropping the client and recreating it when setting the read pointer (which is needed because there seems to be no way of aborting an ongoing request to the node)
• Removed "read requests" from the follow task so the follow task is now only responsible for fetching chain updates and setting the read pointer when requested

read_block and read_block_range

Follower::read_block and Follower::read_block_range now spawn futures and return join handles to make it possible to make read requests concurrently while not depending on the follower's background task.

New examples

• Added set_read_pointer example that shows changing the follower's read pointer while following the chain
• Added concurrent_reads example that shows how to read chain blocks concurrently

Breaking Changes

• Some variants of the crate's Error type were renamed/removed
• ReadBlock and ReadBlockRange implement Future and should be awaited directly, i.e.: follower.read_block().await instead of follower.read_block().read().await

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[bkioshn]

Looks good to me. Quite clear after taking a look at the code after the last tech discussion. Just a few grammar error (:

[stevenj]

LGTM, added suggestions for the grammar issues @bkioshn already mentioned.

[stevenj]

LGTM