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

using ActionList = Action[MAX_ACTIONS];
    
    template <typename Fn>
    void ForEachMergeSetup(Fn&& fn)
    {
        ActionList arg_actions = {};
        
        ForEachNoDup(arg_actions, SET, NEGATE, [&] {
            ActionList conf_actions = {};
            ForEachNoDup(conf_actions, SET, SECTION_NEGATE, [&] {
                for (bool soft_set : {false, true}) {
                    for (bool force_set : {false, true}) {
                        for (const std::string& section : {CBaseChainParams::MAIN, CBaseChainParams::TESTNET, CBaseChainParams::SIGNET}) {
                            for (const std::string& network : {CBaseChainParams::MAIN, CBaseChainParams::TESTNET, CBaseChainParams::SIGNET}) {
                                for (bool net_specific : {false, true}) {
                                    fn(arg_actions, conf_actions, soft_set, force_set, section, network, net_specific);
                                }
                            }
                        }
                    }
                }
            });
        });
    }
    
    std::vector<std::string> GetValues(const ActionList& actions,