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

CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
        ssTx << psbtx;
        result.pushKV("psbt", EncodeBase64(ssTx.str()));
    }
    result.pushKV("origfee", ValueFromAmount(old_fee));
    result.pushKV("fee", ValueFromAmount(new_fee));
    UniValue result_errors(UniValue::VARR);
    for (const bilingual_str& error : errors) {
        result_errors.push_back(error.original);
    }
    result.pushKV("errors", result_errors);
    return result;
},
    };
}
static RPCHelpMan bumpfee() { return bumpfee_helper("bumpfee"); }
static RPCHelpMan psbtbumpfee() { return bumpfee_helper("psbtbumpfee"); }
static RPCHelpMan rescanblockchain()
{
    return RPCHelpMan{"rescanblockchain",
                "\nRescan the local blockchain for wallet related transactions.\n"
                "Note: Use \"getwalletinfo\" to query the scanning progress.\n",
                {
                    {"start_height", RPCArg::Type::NUM, RPCArg::Default{0}, "block height where the rescan should start"},
                    {"stop_height", RPCArg::Type::NUM, RPCArg::Optional::OMITTED_NAMED_ARG, "the last block height that should be scanned. If none is provided it will rescan up to the tip at return time of this call."},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::NUM, "start_height", "The block height where the rescan started (the requested height or 0)"},