[fix] correct addition of of the spmd submodule to onedal.__all__ to follow proper importing standards

[icfaust]

Description

Should correct issues of importing using from onedal import * when an spmd backend is available and someone actually wants to use it that way. Doing sub sub modules in an all will mess with things. (https://docs.python.org/3/tutorial/modules.html#importing-from-a-package)

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Checklist:

Completeness and readability

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes or created a separate PR with updates and provided its number in the description, if necessary.
• Git commit message contains an appropriate signed-off-by string (see CONTRIBUTING.md for details).
• I have resolved any merge conflicts that might occur with the base branch.

Testing

• I have run it locally and tested the changes extensively.
• All CI jobs are green or I have provided justification why they aren't.
• I have extended testing suite if new functionality was introduced in this PR.

Performance

• I have measured performance for affected algorithms using scikit-learn_bench and provided at least a summary table with measured data, if performance change is expected.
• I have provided justification why performance and/or quality metrics have changed or why changes are not expected.
• I have extended the benchmarking suite and provided a corresponding scikit-learn_bench PR if new measurable functionality was introduced in this PR.

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
onedal/spmd/__init__.py	77.77%	0 Missing and 2 partials ⚠️

Flag	Coverage Δ
azure	82.05% <77.77%> (+0.01%)	⬆️
github	74.36% <ø> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
onedal/__init__.py	77.01% <ø> (+1.18%)	⬆️
onedal/spmd/__init__.py	77.77% <77.77%> (-22.23%)	⬇️

... and 1 file with indirect coverage changes

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[icfaust]

/intelci: run

[icfaust]

/intelci: run