values smaller than 0.001 sat/B can't be represented by CFeeRate, but they are not rejected.

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.0009

error code: -6
error message:
Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)
```

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.000000000009

error code: -3
error message:
Invalid amount

{
        UniValue obj(UniValue::VOBJ);
        obj.pushKV("isscript", true);
        obj.pushKV("iswitness", true);
        obj.pushKV("witness_version", 0);
        obj.pushKV("witness_program", HexStr(id));
        return obj;
    }
    UniValue operator()(const WitnessUnknown& id) const
    {
        UniValue obj(UniValue::VOBJ);
        obj.pushKV("iswitness", true);
        obj.pushKV("witness_version", (int)id.version);
        obj.pushKV("witness_program", HexStr(Span<const unsigned char>(id.program, id.length)));
        return obj;
    }
};
UniValue DescribeAddress(const CTxDestination& dest)
{
    return std::visit(DescribeAddressVisitor(), dest);
}
unsigned int ParseConfirmTarget(const UniValue& value, unsigned int max_target)