server/internal: copy bmizerany/ollama-go to internal package (#9294)

This commit copies (without history) the bmizerany/ollama-go repository
with the intention of integrating it into the ollama as a replacement
for the pushing, and pulling of models, and management of the cache they
are pushed and pulled from.

New homes for these packages will be determined as they are integrated
and we have a better understanding of proper package boundaries.

server/internal/client/ollama/trace.go

@@ -0,0 +1,48 @@
+package ollama
+
+import (
+	"context"
+)
+
+// Trace is a set of functions that are called to report progress during blob
+// downloads and uploads.
+type Trace struct {
+	// Update is called during [Registry.Push] and [Registry.Pull] to
+	// report the progress of blob uploads and downloads.
+	//
+	// It is called once at the beginning of the download with a zero n and
+	// then once per read operation with the number of bytes read so far,
+	// and an error if any.
+	//
+	// A function assigned must be safe for concurrent use. The function is
+	// called synchronously and so should not block or take long to run.
+	Update func(_ *Layer, n int64, _ error)
+}
+
+func (t *Trace) update(l *Layer, n int64, err error) {
+	if t.Update != nil {
+		t.Update(l, n, err)
+	}
+}
+
+type traceKey struct{}
+
+// WithTrace returns a context derived from ctx that uses t to report trace
+// events.
+func WithTrace(ctx context.Context, t *Trace) context.Context {
+	return context.WithValue(ctx, traceKey{}, t)
+}
+
+var emptyTrace = &Trace{}
+
+// traceFromContext returns the Trace associated with ctx, or an empty Trace if
+// none is found.
+//
+// It never returns nil.
+func traceFromContext(ctx context.Context) *Trace {
+	t, _ := ctx.Value(traceKey{}).(*Trace)
+	if t == nil {
+		return emptyTrace
+	}
+	return t
+}