Add longitude roll primitives for prime-meridian-crossing domains

[frodre]

PR 2 of 5 in the prime-meridian longitude stack. Adds the pure coordinate/data rolling utilities needed to re-express a global grid in a seam-crossing domain's convention. These have no production callers yet — later PRs wire them into the data and model layers — so they are reviewable in isolation with full unit coverage. The interval-based roll only triggers when an interval actually crosses the seam (start < 0 or stop > 360), so in-range intervals are a no-op and non-global grids are left untouched.

Primitives overview (PR #1235)

These primitives are always used as a pair: find_roll_anchor (or find_roll_anchor_from_interval) computes the roll amount once; callers pass it to all subsequent roll_lon_coords and roll_lon_data so coordinates and field tensors shift by the same amount.

Two downstream pathways use them:

• Dataset load — rolls each loaded grid into the user's configured lon_extent convention (PR Roll seam-crossing longitudes in the downscaling data layer #1236)
• Model setup — rolls the model's fine grid to match the incoming coarse batch's convention (PR Add with_rolled_lon to downscaling models #1237)

Changes:

• fme.downscaling.data.utils: add ClosedInterval.finite_values, _requires_lon_roll, coords_require_lon_roll, find_roll_anchor, find_roll_anchor_from_interval, roll_lon_coords, roll_lon_data, and private helpers _validate_rollable_lon and _validate_monotonic_lon.
  • roll_lon_coords (1-D coordinate tensor) and roll_lon_data (N-D field tensor) form a parallel pair: both apply the same roll amount, but roll_lon_coords also remaps values to keep the result monotonically increasing, while roll_lon_data is a pure cyclic shift. Callers pre-compute the roll amount once via find_roll_anchor and pass it to both.
  • roll_latlon_coords is not included here; it operates on a LatLonCoordinates struct rather than a raw tensor and belongs in the PR that first uses it.
• fme.downscaling.data (__init__): export the new roll helpers.
• fme.downscaling.data.test_utils: unit tests for roll amounts, seam-crossing conventions, round-trip invertibility, non-global/non-uniform rejection, and invalid input validation.
• Tests added
• If dependencies changed, "deps only" image rebuilt and "latest_deps_only_image.txt" file updated

Base: refactor/moe-validate-experts-init (PR 1)

Stack

PR	Head → Base	Title
#1234	refactor/moe-validate-experts-init → main	Validate expert grid compatibility in DenoisingMoEPredictor.__init__
#1235	feature/lon-roll-primitives → PR1	Add longitude roll primitives
#1236	feature/lon-roll-data-layer → PR2	Roll seam-crossing longitudes in the data layer
#1237	feature/lon-roll-model → PR3	Add with_rolled_lon to models
#1238	feature/lon-roll-integration → PR4	Roll the model in inference/predict/evaluator

[AnnaKwa]

LGTM, a couple comments.

[AnnaKwa]

Can this functionality go into fme.core so that in the future ACE code can use it to? IIRC it also cannot handle saving windows across the prime meridian?

[frodre]

Yes, I think that will be the plan once we move to integrate this into the dataset writing for ACE. ClosedInterval would also have to be moved, so I think this should go in a separate PR instead of partially moving things and then cleaning up later.

[AnnaKwa]

Nit: the name sounds like it does the action 'roll longitude data' which could be confused with rolling the lon coords. Something like roll_data_along_lon would sound more distinct.