Raise actionable errors for unsupported calibration heuristics

[uriahf]

What changed

• adds early validation for heuristic combinations that create_calibration_curve_times() currently skips internally
• raises a targeted error for censoring_heuristic='adjusted' and competing_heuristic='adjusted_as_censored'
• points users to a supported combination instead of allowing all horizons to be skipped and ending with the generic No data remaining after applying heuristics and time horizons. error
• routes the top-level rtichoke calibration imports through the calibration package API so the validation applies to the documented public entry point
• adds a regression test for the previously silent adjusted case

Why

The current implementation deliberately skips those heuristic choices, but the final error describes an empty-data symptom rather than the unsupported input that caused it. This PR makes the existing contract explicit without changing calibration statistics or choosing a new default.

Scope

This PR does not add a default heuristics_sets value. Choosing a calibration-specific default is a separate API/statistical decision and should not be bundled with error handling.

[github-actions]

PR Preview Action v1.8.1
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2026-08-12 06:14 UTC