fix: keep reversed axes reversed and sort reversed cube viewports

[jvdd]

Fixes items 1 and 4 of #81. Item 3 was already fixed on main by d370e8f (test TestAgentReadback::test_apply_updates_the_lock_controls). Item 2 is covered by #110. Item 5 needs a design and is not in this PR.

Change

• Item 1. syncLayoutViewport set autorange: true on every axis without a viewport key, so a reversed axis rendered normal. A new declaredAutorange reads the figure layout from the spec (Plotly writes autorange: true back into the layout it draws) and follows the rule of _axis_reversed in spec.py: any autorange that contains "reversed", or a fixed range given high to low, gives "reversed". The fixed bounds are still dropped, as before. So "min reversed" and "max reversed" also give "reversed": without their fixed end, Plotly draws them at a default range.
• Direction of a stored range. A new orientedRange orders every range the client writes to Plotly (syncLayoutViewport and fvApplyAxisLocks) by the declared direction. A stored viewport or lock range holds only its bounds, so one given low to high, for example through flexvizApply, still draws a reversed axis reversed.
• Item 4. FlexEngine.build_cubes now normalizes reversed viewport pairs, like FlexEngine.process. Both call one helper, _normalize_viewports, first.
• The client cube key (_fvCubeViewportDomain) sorts the pair too. Without this, the key of a reversed source never matched the sorted server header.
• Separate commit: fvApplyAxisLocks loses its unused changedAxisId parameter and branch. No caller passed it, and the branch wrote autorange: true.
• Architecture.md describes reversed axes and the ingestion step.

Impact

• fig.update_layout(xaxis={"autorange": "reversed"}) (or "min reversed", "max reversed", or a fixed range given high to low) renders reversed on the first render, and stays reversed after a zoom, a panel reset, a double-click autorange, a global reset and an axis lock.
• A viewport or lock range given low to high on a reversed axis draws the axis reversed. A range given high to low on a normal axis now draws it normal.
• A live brush on a zoomed, reversed, cacheable source now filters the target. Before, the server built a range filter with lo > hi, so the preview and the commit showed no rows, and with only the server fix the client would refuse every cube for that source.
• The same view gives the same server cube key for both viewport orders.

Tests

• TestReversedAxisBrowser::test_reversed_axis_survives_zoom_and_reset, for autorange: "reversed", for range: [999, 0], and for "min reversed" and "max reversed" with a fixed end. The first two fail before the item 1 commit, the last two before the commit that makes them "reversed".
• TestReversedAxisBrowser::test_range_given_low_to_high_draws_reversed, for a viewport and for a lock range set through flexvizApply. Both fail before the orientedRange commit.
• test_cube_server.py::test_reversed_viewports_resolve_like_ascending_ones: the cube header for reversed viewports equals the header for ascending ones. Fails before the fix.
• test_browser_cube.py::test_reversed_zoomed_source_live_updates: a live brush on a reversed, zoomed source sends one cube request and filters the target to some of its rows. Fails before the fix (the target sums to 0).
• On this branch merged with main: pytest tests: 2290 passed, 1 skipped. pytest -m browser tests: 330 passed, 12 skipped.

[codspeed]

Merging this PR will not alter performance

✅ 31 untouched benchmarks

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_{Comparing fix/axis-handling-gaps (087ade9) with main (a64c949)}