Support Go 1.23 iterators for the ZADD command

[rueian]

We support Go 1.23 iterators for HMSET, HSET, and XADD:

rueidis/internal/cmds/iter.go

Lines 7 to 26 in fc348f5

	func (c HmsetFieldValue) FieldValueIter(seq iter.Seq2[string, string]) HmsetFieldValue {
	for field, value := range seq {
	c.cs.s = append(c.cs.s, field, value)
	}
	return c
	}
	func (c HsetFieldValue) FieldValueIter(seq iter.Seq2[string, string]) HsetFieldValue {
	for field, value := range seq {
	c.cs.s = append(c.cs.s, field, value)
	}
	return c
	}
	func (c XaddFieldValue) FieldValueIter(seq iter.Seq2[string, string]) XaddFieldValue {
	for field, value := range seq {
	c.cs.s = append(c.cs.s, field, value)
	}
	return c
	}

It would be better to add support for ZADD as well.