FIX, DOC: Fix forest predict_proba with array API and document limitations in coverage

[david-cortes-intel]

Description

Fixes an issue where predict_proba from forest ensembles was returning the wrong class, and along the way adds a section describing the limitations in array API support for estimators like these.

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Checklist:

Completeness and readability

• 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.

[david-cortes-intel]

/intelci: run

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
onedal/ensemble/forest.py	80.00%	1 Missing ⚠️

Flag	Coverage Δ
azure	79.85% <80.00%> (ø)
github	81.87% <80.00%> (-0.02%)	⬇️

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

Files with missing lines	Coverage Δ
onedal/ensemble/forest.py	93.26% <80.00%> (ø)

... and 1 file with indirect coverage changes

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