[App] Add automatic conversion to structures

[tchaton]

What does this PR do?

The user Ross Johnstone got an un-expected behaviour trying to use a list / dict of works. This PR removes the friction by automatically converting to structures internally.

Here is what this feature enable.

class FlowWiStructures(LightningFlow):
    def __init__(self):
        super().__init__()

        self.ws = [EmptyFlow(), EmptyFlow()]

        self.ws = {"a": EmptyFlow(), "b": EmptyFlow()}

    def run(self):
        pass

Fixes #<issue_number>

Does your PR introduce any breaking changes? If yes, please list them.

Before submitting

• Was this discussed/approved via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

PR review

Anyone in the community is welcome to review the PR.
Before you start reviewing, make sure you have read the review guidelines. In short, see the following bullet-list:

• Is this pull request ready for review? (if not, please submit in draft mode)
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Did you have fun?

Make sure you had fun coding 🙃

cc @Borda

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 lightning_app: Tests workflow

Check ID	Status
app-pytest (macOS-11, app, 3.8, latest)	success	✅
app-pytest (macOS-11, app, 3.8, oldest)	success	✅
app-pytest (macOS-11, lightning, 3.9, latest)	success	✅
app-pytest (ubuntu-20.04, app, 3.8, latest)	success	✅
app-pytest (ubuntu-20.04, app, 3.8, oldest)	success	✅
app-pytest (ubuntu-20.04, lightning, 3.9, latest)	success	✅
app-pytest (windows-2022, app, 3.8, latest)	success	✅
app-pytest (windows-2022, app, 3.8, oldest)	success	✅
app-pytest (windows-2022, lightning, 3.8, latest)	success	✅

These checks are required after the changes to src/lightning_app/core/flow.py, tests/tests_app/structures/test_structures.py.

🟢 lightning_app: Examples

Check ID	Status
app-examples (macOS-11, app, 3.9, latest)	success	✅
app-examples (macOS-11, app, 3.9, oldest)	success	✅
app-examples (macOS-11, lightning, 3.9, latest)	success	✅
app-examples (ubuntu-20.04, app, 3.9, latest)	success	✅
app-examples (ubuntu-20.04, app, 3.9, oldest)	success	✅
app-examples (ubuntu-20.04, lightning, 3.9, latest)	success	✅
app-examples (windows-2022, app, 3.9, latest)	success	✅
app-examples (windows-2022, app, 3.9, oldest)	success	✅
app-examples (windows-2022, lightning, 3.9, latest)	success	✅

These checks are required after the changes to src/lightning_app/core/flow.py.

🟢 lightning_app: Azure

Check ID	Status
App.cloud-e2e	success	✅

These checks are required after the changes to src/lightning_app/core/flow.py.

🟢 lightning_app: Docs

Check ID	Status
make-doctest (app)	success	✅
make-html (app)	success	✅

These checks are required after the changes to src/lightning_app/core/flow.py.

🟢 mypy

Check ID	Status
mypy	success	✅

These checks are required after the changes to src/lightning_app/core/flow.py.

🟢 install

Check ID	Status
install-pkg (ubuntu-22.04, app, 3.7)	success	✅
install-pkg (ubuntu-22.04, app, 3.10)	success	✅
install-pkg (ubuntu-22.04, lite, 3.7)	success	✅
install-pkg (ubuntu-22.04, lite, 3.10)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.7)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.10)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.7)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.10)	success	✅
install-pkg (macOS-12, app, 3.7)	success	✅
install-pkg (macOS-12, app, 3.10)	success	✅
install-pkg (macOS-12, lite, 3.7)	success	✅
install-pkg (macOS-12, lite, 3.10)	success	✅
install-pkg (macOS-12, pytorch, 3.7)	success	✅
install-pkg (macOS-12, pytorch, 3.10)	success	✅
install-pkg (macOS-12, lightning, 3.7)	success	✅
install-pkg (macOS-12, lightning, 3.10)	success	✅
install-pkg (windows-2022, app, 3.7)	success	✅
install-pkg (windows-2022, app, 3.10)	success	✅
install-pkg (windows-2022, lite, 3.7)	success	✅
install-pkg (windows-2022, lite, 3.10)	success	✅
install-pkg (windows-2022, pytorch, 3.7)	success	✅
install-pkg (windows-2022, pytorch, 3.10)	success	✅
install-pkg (windows-2022, lightning, 3.7)	success	✅
install-pkg (windows-2022, lightning, 3.10)	success	✅

These checks are required after the changes to src/lightning_app/core/flow.py.

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Thank you for your contribution! 💜

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