resolve conflicts for backport of #20722

marshal.go and marshal_test.go stay as release-23.0 has them: the
upstream change there adapted AppendMarshalSQL's readFloat call, and
that writer does not exist on this branch. parser.go takes the upstream
readFloat wholesale, and parser_test.go keeps this branch's t.Fatalf
style around the widened readFloat return.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Arthur Schreiber <arthur@planetscale.com>

Author: arthurschreiber