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

desc += arg;
            }
        }
        desc += "\n";
        out_sha.Write(MakeUCharSpan(desc));
        if (out_file) {
            BOOST_REQUIRE(fwrite(desc.data(), 1, desc.size(), out_file) == desc.size());
        }
    });
    if (out_file) {
        if (fclose(out_file)) throw std::system_error(errno, std::generic_category(), "fclose failed");
        out_file = nullptr;
    }
    unsigned char out_sha_bytes[CSHA256::OUTPUT_SIZE];
    out_sha.Finalize(out_sha_bytes);
    std::string out_sha_hex = HexStr(out_sha_bytes);
    
    
    
    
    
    
    
    
    
    BOOST_CHECK_EQUAL(out_sha_hex, "d1e436c1cd510d0ec44d5205d4b4e3bee6387d316e0075c58206cb16603f3d82");
}
struct ChainMergeTestingSetup : public BasicTestingSetup {
    static constexpr int MAX_ACTIONS = 2;
    enum Action { NONE, ENABLE_TEST, DISABLE_TEST, NEGATE_TEST, ENABLE_REG, DISABLE_REG, NEGATE_REG };