refactor(conductor): make firm, soft readers subtasks

[SuperFluffy]

Summary

Makes the firm and soft readers subtasks of the main exection loop.

Background

Making the celestia (firm) and astria (soft)
readers subtasks of the executor loop is a more
faithful representation of their dependencies:

1. the execution loop can run with either or both present.
2. but the readers cannot run without the
   execution loop present (the tasks do not run at the
   same level of privilege).
3. to fully initialize they the readers depend on
   data provided via the execution loop (rollup genesis
   info and commitment state).

This patch then spins up the readers during initialization
of the execution event loop, which allows removing a lot
of complexity from the conductor codebase:

1. the readers need not explicitly wait for the state to be
   initialized but receive an already initialized state.
2. there is no need for a bespoke channel to dynamically
   set permits (this was needed for dynamic backpressure
   handling by setting the channel capacity after reading the
   celestia variance from the rollup): a standard mpsc channel
   can be instantiated and then passed to the (soft/sequencer)
   reader.

executor::Initialized::run delegates to
executor::Initialized::run_event_loop to separate
the shutdown token from the other arms of the
select macro - this way, an else => {} arm can be
introduced that shuts down executor as a fallback

Changes

• make the firm (celestia) and soft (sequencer) readers subtasks of the executor task
• remove the JoinMap from the conductor::Inner business logic as this is
  now tracked by the executor task
• initialize the reader tasks only after the initial rollup node state is received
• in the executor task, separate the test for shutdown token cancellation
  from its main event loop so that the tokio::select! macro's else => {} arm
  can be used as a fallback.
• remove the bespoke executor::channel for dynamically setting channel
  capacity at runtime (no longer necessary; the channel is initialized later
  after we know its capacity)
• simplify the State watch channel notifying the readers of the latest rollup
  state by removing the StateIsInit and StateNotInit markers (the readers
  now get a fully initialized watch channel).

Testing

These changes should be transparent and not noticeable. The blackbox tests
still pass which implies that the (tested) conductor behavior works.

Changelogs

NOTE: Update before merge

Ensure all relevant changelog files are updated as necessary. See
keepachangelog for change
categories. Replace this text with e.g. "Changelogs updated." or "No updates
required." to acknowledge changelogs have been considered.

Related Issues

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Link any issues that are related, prefer full GitHub links.

closes

[ethanoroshiba]

Few nits, but otherwise LGTM. I think this refactor will be very nice to have!

[Fraser999]

One minor comment only.

[joroshiba]

stamp