Make nodes commit encode error when aggregation script result cannot be encoded as CBOR

[tmpolaczyk]

Issue #2310 describes a radon script whose result cannot be encoded. If that happens, nodes will not commit any value and the data request will probably resolve with "insufficient commits" error. We could have nodes report an "encode" error to detect this case. There is already a RadError::Encode error, we could reuse it or we could create a more specific EncodeAggregationResultToCbor error.

This is the code that decides to ignore this case:

witnet-rust/node/src/actors/chain_manager/mining.rs

Lines 591 to 594 in 2fa9a2f

	Err(e) => {
	log::error!("Couldn't decode tally value from bytes: {}", e);
	actix::fut::err(())
	}

I tried to find similar issues to #2310, which fails to encode integers greater than 2^64-1, but didn't find any yet. But anyway, it would be great to have that in case something unexpectedly breaks in the future.

[tmpolaczyk]

So unfortunately it looks like RadError::Encode is not a valid RadonError, so we cannot use that. Not sure why, but it looks like if we want to fix this issue we will have to introduce new radon error codes.

See the test from this branch:

https://github.com/tmpolaczyk/witnet-rust/tree/encode-encode-error

it fails with an encode error

thread 'actors::chain_manager::mining::tests::encode_error_can_be_encoded' panicked at 'called `Result::unwrap()` on an `Err` value: Encode { from: "RadonTypes", to: "Vec<u8>" }', node/src/actors/chain_manager/mining.rs:1617:12

[aesedepece]

So unfortunately it looks like RadError::Encode is not a valid RadonError, so we cannot use that. Not sure why, but it looks like if we want to fix this issue we will have to introduce new radon error codes.

That one is definitely needed.