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

{
    return RPCHelpMan{
                "listunspent",
                "\nReturns array of unspent transaction outputs\n"
                "with between minconf and maxconf (inclusive) confirmations.\n"
                "Optionally filter to only include txouts paid to specified addresses.\n",
                {
                    {"minconf", RPCArg::Type::NUM, RPCArg::Default{1}, "The minimum confirmations to filter"},
                    {"maxconf", RPCArg::Type::NUM, RPCArg::Default{9999999}, "The maximum confirmations to filter"},
                    {"addresses", RPCArg::Type::ARR, RPCArg::Default{UniValue::VARR}, "The bitcoin addresses to filter",
                        {
                            {"address", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "bitcoin address"},
                        },
                    },
                    {"include_unsafe", RPCArg::Type::BOOL, RPCArg::Default{true}, "Include outputs that are not safe to spend\n"
                              "See description of \"safe\" attribute below."},
                    {"query_options", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED_NAMED_ARG, "JSON with query options",
                        {