Add the voting logic for regression detection.

[MohamedBilelBesbes]

This PR contains the following changes:

• It introduces consensus voting: alerts only fire when at least cons_th methods agree within a margin index window
• It adds two voting strategies: equal (all methods weighted equally) and priority (Student detections take precedence, equal voting as fallback)
• It has a deduplication guard that prevents the redundant alerts for adjacent revisions resolving to the same regression based on the margin value
• Alert output is now extended with per-method confidences dict and a detection_method naming field encoding the full voting configuration
• It has new unit tests associated with the voting logic
• Older obsolete unit tests are removed
• replicates usage logic is fully propagated in the prototype code

[gmierz]

Great start @MohamedBilelBesbes! Comments below.

[gmierz]

Just need to fix up the migrations, then I think this will be good to land

[MohamedBilelBesbes]

Just need to fix up the migrations, then I think this will be good to land

@gmierz perfect, I squashed the migrations, I think we're good to go.

[gmierz]

r+ great work here @MohamedBilelBesbes!