[tcoratger]

The Beacon API pool and publish endpoints, and the gossip event export, now return the data of each event as its JSON text instead of a parsed value.
This makes the soundness CI job pass again, since the consensus package module no longer imports json.

The problem

The Python boundary check, scripts/check_python_boundary.py, forbids json in a package module: a wrapper passes typed values to the native call and back.
api_post and api_gossip_event parsed the event data with json.loads, so the check failed on master.

The idea

The native calls already return each event as a pair (topic name, JSON data text).
That text is the data field of the Beacon API event stream, and the fork choice event exports api_chain_events and api_fast_confirmation_event return the same pair.
So the two wrappers now return the native pair unchanged, and the tests parse the text themselves.

Example

A valid capella block published to blocks gives the events ("block_gossip", '{"slot":"…","block":"0x…"}') and ("block", '{…,"execution_optimistic":false}').
Before, the second element was a dict; now it is that text, and json.loads gives the same dict as before.

For reviewers

• This breaks Python callers of the two functions; CHANGELOG.md records it under 0.4.0.
• The tests gain two helpers in test_beacon_api_events.py: parsed parses the events of each answer, and gossip_event parses the event of one object.
  The pool and publish tests import parsed; tests that compare only topics are unchanged.
• No allowlist entry is added.

Checks

• scripts/check_python_boundary.py: passes.
• python -m unittest scripts/test_check_python_boundary.py: OK.
• ruff check --no-fix, ruff format --check, ty check: pass.
• scripts/check_python_comments.py --all, scripts/check_docstrings.py: pass.
• pytest on test_beacon_api_publish.py, test_beacon_api_events.py and test_beacon_api_pool.py, with the extension built by uv sync: 490 passed.

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