internal/deephash: increase scratch space size

e66d4e4c81 added AppendTo methods
to some key types. Their marshaled form is longer than 64 bytes.

name    old time/op    new time/op    delta
Hash-8    15.5µs ± 1%    14.8µs ± 1%   -4.17%  (p=0.000 n=9+9)

name    old alloc/op   new alloc/op   delta
Hash-8    1.18kB ± 0%    0.47kB ± 0%  -59.87%  (p=0.000 n=10+10)

name    old allocs/op  new allocs/op  delta
Hash-8      12.0 ± 0%       6.0 ± 0%  -50.00%  (p=0.000 n=10+10)

This is still a bit worse than explicitly handling the types,
but much nicer.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

internal/deephash/deephash.go

@@ -23,7 +23,7 @@ import (
 func calcHash(v interface{}) string {
 	h := sha256.New()
 	b := bufio.NewWriterSize(h, h.BlockSize())
-	scratch := make([]byte, 0, 64)
+	scratch := make([]byte, 0, 128)
 	printTo(b, v, scratch)
 	b.Flush()
 	scratch = h.Sum(scratch[:0])