Add binary decoding benchmarks
Add binary decoding benchmarks

```
BenchmarkBinaryDecodingManual-4         10479085               106 ns/op              40 B/op          2 allocs/op
BenchmarkBinaryDecodingHelpers-4         4485451               263 ns/op              64 B/op          4 allocs/op
BenchmarkBinaryDecodingRow-4             1999726               587 ns/op              96 B/op          5 allocs/op
```

jackc/pgx,jackc/pgx,jackc/pgx,jackc/pgx