Add TransactionView::summary() method

[hdevalence]

Is your feature request related to a problem? Please describe.

There are many applications where it would be useful to display a summary of a transaction's effects on the balances of various accounts, both pre- and post-confirmation:

• Pre-confirmation: in an approval dialog, for showing an exact preview of the effects of a transaction
• Post-confirmation: in a frontend, for showing a summary of what a transaction did

This logic should be implemented once, in the Rust code, so that it can be standardized across the Penumbra ecosystem.

Describe the solution you'd like

• The Balance struct improperly has a derived Serde representation. This is a bug and a violation of our serialization policy. Verify that this was never used. Define a Protobuf message for the Balance struct and use that as the serialization format.

• Define a new Protobuf message and corresponding domain type, penumbra.core.transaction.v1.TransactionSummary, something like (sketch):

message TransactionSummary {
    message Effects {
        core.keys.v1.AddressView address = 1;
        core.asset.v1.Balance balance = 2;
    }
    repeated Effects effects = 1;
}

• Define a new method TransactionView::summary(&self) -> TransactionSummary that produces a TransactionSummary, iterating through each visible action and collecting the effects of the transaction. This should preserve the info available in the AddressViews about the meaning of the addresses.

[TalDerei]

step towards penumbra-zone/web#1394 cc @grod220

[erwanor]

This was done for Output/Spend/Swap/SwapClaim views in #4943. Adding the LP ones might enable some cool use cases, but afaict this is complete.