fix(backend): call vram.EstimateModelMultiContext (master build broken: undefined vram.EstimateModel) (#10426)

fix(backend): call vram.EstimateModelMultiContext for model size estimate

core/backend/options.go called vram.EstimateModel, which does not exist in
the vram package (it exposes EstimateModelMultiContext). This broke the build
on master (undefined: vram.EstimateModel). Use EstimateModelMultiContext with
a nil context-size slice (defaults to a single 8192 estimate); the returned
MultiContextEstimate.SizeBytes is exactly what the caller consumes, so size
estimation behavior is unchanged.

Assisted-by: Claude:claude-opus-4-8

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

core/backend/options.go

@@ -90,7 +90,7 @@ func estimateModelSizeBytes(c config.ModelConfig, modelsPath string) int64 {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 
-	result, err := vram.EstimateModel(ctx, input)
+	result, err := vram.EstimateModelMultiContext(ctx, input, nil)
 	if err != nil || result.SizeBytes == 0 {
 		return 0
 	}