[PierreRaybaut]

Closes #99

Summary

The selection of image pixels by regions of interest (rule sigima.image.roi.pixel_centers, IMAGE_ROI_CONVENTION, #89) was recorded in the execution context only when an input image carried regions of interest. The operations taking their regions of interest as parameters — extract_roi, extract_rois, erase, offset_correction — are usually called on images without attached ROIs (DataLab defines them graphically): their description recorded no context, and a replay of such a call recorded before Sigima 1.4 (which selected other pixels) was accepted, reporting a different result instead of being refused.

• image_roi_convention(inputs, contract=None): also returns the rule when the contract has an image input and a ROI2DParam parameter (single, list or both), whatever the inputs — a static property of the operation, read from its contract.
• describe_call and prepare_execution pass the contract: the rule is recorded and, for a replay, checked (unsupported_context when missing or another version).
• No version change: the rule (version 1) is unchanged, it is recorded in more cases; the contract versions are unchanged. Signal ROI parameters (ROI1DParam) are not concerned.
• Docs: module docstrings, guidelines, user guide (contracts), release note — with French translations (checked with a gettext build + sphinx_intl update: no change).

Validation

• New tests: for the 4 operations on an image without ROI (single and list parameters), the description and the preparation record the rule, a replay with the recorded context gives the same result, replays with a context recorded before Sigima 1.4 ({}, {"x_alignment": None}, {"roi_convention": None}) or another rule version are refused; a registry-wide guard checks that exactly these 4 operations are detected; signal extract_roi records nothing.
• Full suite: 2340 passed; --qualification-report: no problem (the 4 operations qualified, validation and replay passed).
• DataLab develop against this branch: provenance, replay and capsule tests pass (138).
• DataLab-Capsule needs no change: it records the context mapping of the description since Record the execution context declared by the computation library DataLab-Capsule#4.