Standardize linting and formatting

[MasterSkepticista]

Note: This PR only impacts openfl.experimental namespace, and should be a non-breaking change.

Changes:

• Sorted imports using isort
• Formatted files using black
• Linted using flake8

Configuration for isort and black is included in pyproject.toml. flake8 continues to use setup.cfg

For future development:

• Lint using ./shell/lint.sh
• Format using ./shell/format.sh
• Use absolute imports as discussed here.

[psfoley]

Thanks @MasterSkepticista. Looks like there's just a couple remaining lint issues before approval. Will the namex changes be included in a future PR?

[MasterSkepticista]

Yes, this PR is for non-breaking formatting changes. namex will impact API surface, and may impact project structure. That will be for a future PR.

[MasterSkepticista]

@psfoley Added relevant ignores in setup.cfg

Could not get rid of F821 without invoking other warnings. noqa: # does not seem to work with multi-line code.
How does ModelHeader and TensorProto not throw an error when code reaches there? The error is valid, no definitions for those are imported anywhere in the file.

[psfoley]

Changing the import order is leading to this circular import error (confirmed this by changing the order manually locally on develop, which is passing). This should either be reverted or fixed: https://github.com/securefederatedai/openfl/actions/runs/9381169993/job/25829824994?pr=980#step:5:19

[MasterSkepticista]

Since __init__.py files are useful for API exports, until we transition to API export decorators, we need to:

• Export classes using absolute paths:

# Before (order-sensitive, fails)
from .federated_runtime import FederatedRuntime
from .local_runtime import LocalRuntime
from .runtime import Runtime
__all__ = ["FederatedRuntime", "LocalRuntime", "Runtime"]

# After (order-agnostic)
from openfl.experimental.runtime.federated_runtime import FederatedRuntime
from openfl.experimental.runtime.local_runtime import LocalRuntime
from openfl.experimental.runtime.runtime import Runtime

• Use absolute imports in source code:

# Before (order sensitive, fails)
from openfl.experimental.runtime import Runtime

# After (order-agnostic)
from openfl.experimental.runtime.runtime import Runtime

This gives the intended behavior: users can access imported objects without long paths in user code, and order of imports within source code does not lead to errors.

This fix will be used for all subsequent tests.

[MasterSkepticista]

Fixed imports in the entire openfl.experimental interface.