Support [n]byte/[]byte type Scan/Append to FixedString column

[rogeryk]

Summary

Support [n]byte/[]byte type Scan/Append to FixedString column

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added

closes #1155

[jkaflik]

Why copy instead of assign slice?

[rogeryk]

The length of slice may not equal col.col.Size. Use copy to cover overlap scenarios

[jerbob92]

Just to let you know: this has broken our code to save XID's as FixedString(20) in CH. This is due to that the XID is actually an alias for a byte array (type ID [rawLen]byte), so it's now hitting the new code. XID's in byte format are 12 bytes, but in string format it's 20. Since XID has implemented the driver.Valuer interface, it would normally have hit this block:

if s, ok := v.(driver.Valuer); ok {
	val, err := s.Value()
	if err != nil {
		return &ColumnConverterError{
			Op:   "AppendRow",
			To:   "FixedString",
			From: fmt.Sprintf("%T", s),
			Hint: "could not get driver.Valuer value",
		}
	}
	return col.AppendRow(val)
}

Internally, this would stringify the XID and thus make them a length of 20.

But since this change it's hitting the byte array block and resulting in the following error:

clickhouse [AppendRow]: converting xid.ID to FixedString is unsupported. invalid size 12, expect 20

My suggestion would be to move the handling of the byte array to below the driver.Valuer/Stringer handling, imho in case of FixedString, the driver.Valuer/Stringer handling should have precedence over other handling.

[rogeryk]

@jerbob92 Sounds right, I think should create a new issue and file a PR to fix it.

[jerbob92]

@rogeryk or maybe @jkaflik should revert it and you should make a new PR...