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

{
            std::string flags = "";
            for (auto& it : WALLET_FLAG_MAP)
                if (it.second & MUTABLE_WALLET_FLAGS)
                    flags += (flags == "" ? "" : ", ") + it.first;
    return RPCHelpMan{"setwalletflag",
                "\nChange the state of the given wallet flag for a wallet.\n",
                {
                    {"flag", RPCArg::Type::STR, RPCArg::Optional::NO, "The name of the flag to change. Current available flags: " + flags},
                    {"value", RPCArg::Type::BOOL, RPCArg::Default{true}, "The new state."},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::STR, "flag_name", "The name of the flag that was modified"},
                        {RPCResult::Type::BOOL, "flag_state", "The new state of the flag"},
                        {RPCResult::Type::STR, "warnings", "Any warnings associated with the change"},
                    }
                },
                RPCExamples{
                    HelpExampleCli("setwalletflag", "avoid_reuse")
                  + HelpExampleRpc("setwalletflag", "\"avoid_reuse\"")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{