Add cross_channel=False warning in case covariates exist

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• sdm/models/kumo/timeseries/forecast/model.py

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📝 Summary

Summary by CodeRabbit

• Behavior
  • A one-time warning now appears when historical context-only columns are provided while cross-channel forecasting is disabled. Forecasting continues with those columns included.

KumoForecast._forward now warns once when historical context-only columns are present and cross_channel is disabled. It continues to concatenate those columns with target history.

Changes: Forecast context warning

Layer / File(s)	Summary
Forward-path warning sdm/models/kumo/timeseries/forecast/model.py	_forward warns once when context-only historical columns are nonempty and cross_channel is None. The existing concatenation with target history remains unchanged.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Merge Risk: ⚪ Minimal · up to cb8f3

With cross-channel attention disabled, context-only columns do not affect target forecasts; the warning explains this limitation. No actionable merge risk was identified.

Pre-merge checks: 3 · 1 · 1

Failed checks: 1 warning · 1 inconclusive

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check		No pull request description was provided, so the change intent and validation details are not documented beyond the title.	Add a brief description that explains the warning behavior, the affected condition, and the expected handling of historical context-only columns.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly describes the main change: adding a warning when covariates exist while cross_channel is disabled.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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