ProtoJSON regression in Serde derives

[hdevalence]

We noticed a regression since #95 (not sure where or when exactly) that results in the ibc-proto types having broken Serialize, Deserialize implementations.

Test case:

• https://github.com/penumbra-zone/penumbra/blob/timeout-bug/crates/wasm/tests/test_deserialize.rs fails (but should pass)
• https://github.com/penumbra-zone/penumbra/blob/timeout-bug-snakecase/crates/wasm/tests/test_deserialize.rs passes (but should fail)

In that test code, the Ics20Withdrawal is a Penumbra-specific action that includes an IBC TimeoutHeight. Our Proto build configuration place the ibc-proto types as the generated code for ibc proto messages, so its Serialize and Deserialize impls forward to the ones in this crate.

Looking at the code in https://github.com/cosmos/ibc-proto-rs/blob/main/tools/proto-compiler/src/cmd/compile.rs , I don't see any invocations of pbjson_build at all, I'm not sure what happened since #95.