abci Tag deserializer

[ancazamfir]

DeliverTx and rpc block_result Response include events in the form Vec<Event>, where Event is defined here like this:

/// Event
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct Event {
    /// Event type
    #[serde(rename = "type")]
    pub type_str: String,

    /// Attributes
    pub attributes: Vec<Tag>,
}

Where Tag is defined here
The Tag fields are base64 encoded but we do not decode when deserializing them, so the the Event looks something like:

    type_str: "send_packet",
    attributes: [
        Tag {
            key: Key(
                "cGFja2V0X3RpbWVvdXRfaGVpZ2h0",
            ),
            value: Value(
                "MC00ODQw",
            ),
        },
...

instead of:

Event {
    type_str: "send_packet",
    attributes: [
        Tag {
            key: Key(
                "packet_timeout_height",
            ),
            value: Value(
                "0-4840",
            ),
        },
...

In IBC we need to extract some info from these tags (in particular the ones in DeliverTx) so we currently have to do something like:

let key = String::from_utf8(base64::decode(tag.key.to_string().as_bytes())?)?;

I think this should be done in tendermint-rs instead.