fix: Allow MultiCOGLayer sampler to be overridden from default linear

[willjnz]

Related to #215 (comment). My data is UInt16 surface reflectance with nodata=0.

Can be simply used like

new MultiCOGLayer({
  ...
  bandSampler: { minFilter: "nearest", magFilter: "nearest" },
}),

Before (Linear sampler - blurred, with artifacts)	After (Nearest sampler - sharp, clean)

[earlybard]

+1, we need this for MultiCOGLayer too. We composite Int16 reflectance and discard nodata with an exact-match filter; with linear sampling every scene edge and nodata hole gets a one-texel rim where the sentinel blends into real data and slips past the filter. Nearest fixes it. It also means r32float bands (#650) don't need OES_texture_float_linear.