sql/pgwire: Avoid bytes.Reader in decodeOidDatum for binary formats
sql/pgwire: Avoid bytes.Reader in decodeOidDatum for binary formats

This avoids the inherent allocation in `bytes.NewReader`, and avoids the
need to use reflection for float values.

maxlang/cockroach,glycerine/cockroach,paperstreet/cockroach,petermattis/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,petermattis/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,petermattis/cockroach,veteranlu/cockroach,maxlang/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,paperstreet/cockroach,maxlang/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,petermattis/cockroach,maxlang/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,veteranlu/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,petermattis/cockroach,petermattis/cockroach,glycerine/cockroach,glycerine/cockroach,veteranlu/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,maxlang/cockroach,veteranlu/cockroach,cockroachdb/cockroach,glycerine/cockroach,vaibhavarora/cockroach,petermattis/cockroach,glycerine/cockroach,maxlang/cockroach,veteranlu/cockroach,veteranlu/cockroach,paperstreet/cockroach,cockroachdb/cockroach,glycerine/cockroach,cockroachdb/cockroach,glycerine/cockroach,glycerine/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,maxlang/cockroach,paperstreet/cockroach,maxlang/cockroach,petermattis/cockroach