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

result.pushKV("fee", ValueFromAmount(fee));
    result.pushKV("changepos", change_position);
    return result;
},
    };
}
RPCHelpMan signrawtransactionwithwallet()
{
    return RPCHelpMan{"signrawtransactionwithwallet",
                "\nSign inputs for raw transaction (serialized, hex-encoded).\n"
                "The second optional argument (may be null) is an array of previous transaction outputs that\n"
                "this transaction depends on but may not yet be in the block chain." +
        HELP_REQUIRING_PASSPHRASE,
                {
                    {"hexstring", RPCArg::Type::STR, RPCArg::Optional::NO, "The transaction hex string"},
                    {"prevtxs", RPCArg::Type::ARR, RPCArg::Optional::OMITTED_NAMED_ARG, "The previous dependent transaction outputs",
                        {
                            {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "",
                                {
                                    {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
                                    {"vout", RPCArg::Type::NUM, RPCArg::Optional::NO, "The output number"},
                                    {"scriptPubKey", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "script key"},
                                    {"redeemScript", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "(required for P2SH) redeem script"},
                                    {"witnessScript", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "(required for P2WSH or P2SH-P2WSH) witness script"},
                                    {"amount", RPCArg::Type::AMOUNT, RPCArg::Optional::OMITTED, "(required for Segwit inputs) the amount spent"},
                                },
                            },
                        },
                    },
                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"ALL"}, "The signature hash type. Must be one of\n"