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

#include <key_io.h>
#include <outputtype.h>
#include <rpc/util.h>
#include <script/descriptor.h>
#include <script/signingprovider.h>
#include <tinyformat.h>
#include <util/strencodings.h>
#include <util/string.h>
#include <util/translation.h>
#include <tuple>
#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/split.hpp>
const std::string UNIX_EPOCH_TIME = "UNIX epoch time";
const std::string EXAMPLE_ADDRESS[2] = {"bc1q09vm5lfy0j5reeulh4x5752q25uqqvz34hufdl", "bc1q02ad21edsxd23d32dfgqqsz4vv4nmtfzuklhy3"};
void RPCTypeCheck(const UniValue& params,