[ADP-3350] Add Read.ChainTip type

[HeinrichApfelmus]

This pull request adds a data type ChainTip to the Cardano.Wallet.Read hierarchy.

This type ChainTip is used in the ChainSync protocol to advertise the tip of the server's chain. It combines the information of a ChainPoint with a BlockNo.

This pull requests also adds

• Conversions to/from types in ouroboros-consensus for the networking layer

Comments

• The NetworkLayer currently uses the BlockHeader type for advertising the tip of the chain. However, this is strictly speaking incorrect, as the BlockHeader also includes a reference to the previous block header, which ChainTip does not. In the legacy code, we currently invent a value out of thin air — the new type ChainTip is more correct.
• Subsequent pull requests will change the NetworkLayer interface to use Read.ChainPoint and Read.ChainTip.

Issue Number

ADP-3350

[paweljakubas]

looking good 👍