v1.2.0

v1.2.0

New: Sampler for reusable bilinear weights

BilinearValue unpacks the whole field on every call (~408 µs per point on an RDPS rotated grid), which rules it out for rendering, regridding, or reading the same points from many fields on one grid.

• NewSampler(f) builds once per grid; Weights(lat, lon) returns the four corner indices and fractions, and Interpolate applies them to the Values() of any field on that grid.
• Supports templates 3.0, 3.1 and regular 3.40.
• BilinearWeights.Outside flags points beyond the grid edge (clamped to the edge cell, as before).
• NearestCorner() returns the heaviest corner for categorical fields such as precipitation type.
• Sampler.Matches(f) checks that a field shares the grid.
• BilinearValue is now built on the same weights/interpolate steps with the same arithmetic order, so its results are unchanged.

Verification

Sampler results are bit-identical to BilinearValue, errors included, across 69 decodable fixture grids (57 on 3.0, 4 on 3.1, 8 on 3.40). The existing suite passes unchanged.

lookup	cost per point
BilinearValue	408 µs
Sampler.Weights + Interpolate	0.21 µs