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 result;
    result.reserve(s.size() * 2);
    for (const char ch: s) {
        if (ch == '\'') {
            result += "'\''";
        } else {
            result += ch;
        }
    }
    return "'" + result + "'";
}
/**
 * Shell-quotes the argument if it needs quoting, else returns it literally, to save typing.
 *
 * @note This is intended for help, not for security-sensitive purposes.
 */
std::string ShellQuoteIfNeeded(const std::string& s)
{
    for (const char ch: s) {
        if (ch == ' ' || ch == '\'' || ch == '"') {
            return ShellQuote(s);
        }
    }
    return s;
}
}
std::string HelpExampleCli(const std::string& methodname, const std::string& args)