feat(app): 🎣 add missing Dex component hook

[cratelyn]

see #3739, and #4246.

while wiring up a pair of missing component hooks for the Sct component, i found another (noöp) hook that we do not include in the App's control flow.

this isn't currently a bug, since <Dex as Component>::begin_block() is a noöps but could easily lead to a surprising outcome in the future, if more logic was introduced to that trait method.

checklist before requesting a review

• if this code contains consensus-breaking changes, i have added the "consensus-breaking" label. otherwise, i declare my belief that there are not consensus-breaking changes, for the following reason:

  while this does change the control flow of consensus-critical logic, this does not
  change the execution of incoming data. the hooks introduced here are noöps.

[cratelyn]

penumbra/crates/core/component/dex/src/component/dex.rs

Lines 42 to 47 in 3b62d64

	#[instrument(name = "dex", skip(_state, _begin_block))]
	async fn begin_block<S: StateWrite + 'static>(
	_state: &mut Arc<S>,
	_begin_block: &abci::request::BeginBlock,
	) {
	}

for reference: