drop bfloat16 dependency

goos: darwin
goarch: arm64
pkg: github.com/ollama/ollama/convert/bfloat16
cpu: Apple M3 Max
BenchmarkBfloat16/d4l3k/go-bfloat16-16               516           2269453 ns/op
BenchmarkBfloat16/simple-16                          1759            626316 ns/op
PASS
ok      github.com/ollama/ollama/convert/bfloat16        2.502s

convert/bfloat16/bfloat16.go

@@ -0,0 +1,21 @@
+package bfloat16
+
+import "math"
+
+// FromFloat32s converts a slice of float32 values to a slice of bfloat16 values, represented as uint16s.
+func FromFloat32s(f32s []float32) (u16s []uint16) {
+	u16s = make([]uint16, len(f32s))
+	for i := range f32s {
+		u16s[i] = uint16(math.Float32bits(f32s[i]) >> 16)
+	}
+	return u16s
+}
+
+// Float32s converts a slice of bfloat16 values, represented as uint16s, back to a slice of float32 values.
+func Float32s(u16s []uint16) (f32s []float32) {
+	f32s = make([]float32, len(u16s))
+	for i := range u16s {
+		f32s[i] = math.Float32frombits(uint32(u16s[i]) << 16)
+	}
+	return f32s
+}