New Block structure (#3101)

## Motivation

Verifying Linera (micro)chains with a light client requires following
the chain's blocks and subsequently confirming whether an event, a
message, state change, were part of that block. Our current block
definition - `ExecutedBlock` type - was not made for this purpose:
- there is no distinction between block's "metadata" and the "body" -
which would allow for _light_ verification of the blocks.
- the events/messages/operations are all layed out, flat, in the
`BlockExecutionOutcome` w/o a way to easily verify whether a particular
event is part of that set other than sending the whole vector.

## Proposal

In this PR we introduce the new block structures. The new `Block` type
consists of two elements:
- (block) header
- (block) body.

`BlockHeader` is a succint representation of the chain's new block. It
contains metadata that suffices to track the chain's progress:
```rust
pub struct BlockHeader {
    /// The block version.
    pub version: u8, // TODO: More granular versioning. #3078
    /// The chain to which this block belongs.
    pub chain_id: ChainId,
    /// The number identifying the current configuration.
    pub epoch: Epoch,
    /// The block height.
    pub height: BlockHeight,
    /// The timestamp when this block was created.
    pub timestamp: Timestamp,
    /// The hash of the chain's execution state after this block.
    pub state_hash: CryptoHash,
    /// Certified hash of the previous block in the
    /// chain, if any.
    pub previous_block_hash: Option<CryptoHash>,
    /// The user signing for the operations in the block and paying for their execution
    /// fees. If set, this must be the `owner` in the block proposal. `None` means that
    /// the default account of the chain is used. This value is also used as recipient of
    /// potential refunds for the message grants created by the operations.
    pub authenticated_signer: Option<Owner>,

    // Inputs to the block, chosen by the block proposer.
    /// Cryptographic hash of all the incoming bundles in the block.
    pub bundles_hash: CryptoHash,
    /// Cryptographic hash of all the operations in the block.
    pub operations_hash: CryptoHash,

    // Outcome of the block execution.
    /// Cryptographic hash of all the messages in the block.
    pub messages_hash: CryptoHash,
    /// Cryptographic hash of all the oracle responses in the block.
    pub oracle_responses_hash: CryptoHash,
    /// Cryptographic hash of all the events in the block.
    pub events_hash: CryptoHash,
}
```

`BlockBody` holds the data that is not necessary for (light)
verification but was either an input to the block's execution (incoming
bundles, operations) or its output (oracle responses, messages sent,
events emitted). Each vector is deterministically hashed (into
`CryptoHash`) and the result of that hashing is put into the
`BlockHeader`. This way it's possible to verify inclusion of any
specific element w/o having to sent all of the body.

```rust
/// The body of a block containing all the data included in the block.
#[derive(Debug, PartialEq, Eq, Hash, Clone, Serialize, Deserialize, SimpleObject)]
pub struct BlockBody {
    /// A selection of incoming messages to be executed first. Successive messages of same
    /// sender and height are grouped together for conciseness.
    pub incoming_bundles: Vec<IncomingBundle>,
    /// The operations to execute.
    pub operations: Vec<Operation>,
    /// The list of outgoing messages for each transaction.
    pub messages: Vec<Vec<OutgoingMessage>>,
    /// The record of oracle responses for each transaction.
    pub oracle_responses: Vec<Vec<OracleResponse>>,
    /// The list of events produced by each transaction.
    pub events: Vec<Vec<EventRecord>>,
}
```

## Test Plan

All of the tests have been updated to work with the new types.

## Release Plan

- These changes follow the usual release cycle. Although we may want to
defer this update since this change is not backwards compatible.

## Links

- Closes #3077
- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)

---------

Co-authored-by: Andreas Fackler <andreas.fackler@linera.io>

examples/hex-game/tests/hex_game.rs

@@ -31,8 +31,8 @@ async fn hex_game() {
         })
         .await;
 
-    let executed_block = certificate.inner().executed_block();
-    let message_id = executed_block.message_id_for_operation(0, 0).unwrap();
+    let block = certificate.inner().block();
+    let message_id = block.message_id_for_operation(0, 0).unwrap();
     let description = ChainDescription::Child(message_id);
     let mut chain = ActiveChain::new(key_pair1.copy(), description, validator);
 
@@ -105,8 +105,8 @@ async fn hex_game_clock() {
         })
         .await;
 
-    let executed_block = certificate.inner().executed_block();
-    let message_id = executed_block.message_id_for_operation(0, 0).unwrap();
+    let block = certificate.inner().block();
+    let message_id = block.message_id_for_operation(0, 0).unwrap();
     let description = ChainDescription::Child(message_id);
     let mut chain = ActiveChain::new(key_pair1.copy(), description, validator.clone());
 

linera-base/src/crypto.rs

@@ -41,6 +41,14 @@ type HasherOutput = generic_array::GenericArray<u8, HasherOutputSize>;
 #[cfg_attr(with_testing, derive(Default))]
 pub struct CryptoHash(HasherOutput);
 
+/// A vector of cryptographic hashes.
+/// This is used to represent a hash of a list of hashes.
+#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Hash, Serialize, Deserialize)]
+#[cfg_attr(with_testing, derive(Default))]
+pub struct CryptoHashVec(pub Vec<CryptoHash>);
+
+impl<'de> BcsHashable<'de> for CryptoHashVec {}
+
 /// A signature value.
 #[derive(Eq, PartialEq, Copy, Clone)]
 pub struct Signature(pub dalek::Signature);

linera-base/src/data_types.rs

@@ -803,6 +803,8 @@ impl FromStr for OracleResponse {
     }
 }
 
+impl<'de> BcsHashable<'de> for OracleResponse {}
+
 /// Description of the necessary information to run a user application.
 #[derive(Clone, Debug, Deserialize, Eq, PartialEq, Hash, Serialize)]
 pub struct UserApplicationDescription {