fix(pebble): avoid pydantic warning for exec checks

[gcomneno]

Summary

• make the check discriminator handle already-validated check models during serialization
• avoid the PydanticSerializationUnexpectedValue warning when marshalling projects with exec checks
• add a unit test covering Project.marshal() with an exec health check

Issue

• closes Pydantic warning: PydanticSerializationUnexpectedValue #1154

[gcomneno]

Hi! Just gently following up on this one.

I rebased the branch onto current upstream/main and re-ran the focused checks locally:

• uv run --group dev python -m pytest -q tests/unit/test_project.py -rs
• uv run --group lint --group types ruff check rockcraft/pebble.py tests/unit/test_project.py
• uv run --group lint --group types ruff format --check rockcraft/pebble.py tests/unit/test_project.py

The focused test run passes with 80 passed, and Ruff is clean.

Happy to adjust anything else if useful.

[lczyk]

@gcomneno thanks for the PR! :) looks good. i've let the CI run and noticed the linting errors, so here is a PR to your PR where i've tried to placate our type-checking overlords. ff to use or ignore. 🤷‍♀️

not gonna 'request changes' since the PR is sound, but dont wanna quite 'approve' since the linting wants some care.

@tigarmo bump. i'm poking at this because just run into the same thing

[gcomneno]

Thanks @lczyk, I merged your patch and reran the focused checks locally.

Validation:

• uv run --group dev python -m pytest -q tests/unit/test_project.py -rs → 80 passed
• uv run --group lint --group types ruff check rockcraft/pebble.py tests/unit/test_project.py
• uv run --group lint --group types ruff format --check rockcraft/pebble.py tests/unit/test_project.py
• git diff --check

The branch is now updated at 1d898ec.