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

{
    if (wallet.IsLocked()) {
        throw JSONRPCError(RPC_WALLET_UNLOCK_NEEDED, "Error: Please enter the wallet passphrase with walletpassphrase first.");
    }
}
WalletContext& EnsureWalletContext(const std::any& context)
{
    auto wallet_context = util::AnyPtr<WalletContext>(context);
    if (!wallet_context) {
        throw JSONRPCError(RPC_INTERNAL_ERROR, "Wallet context not found");
    }
    return *wallet_context;
}
LegacyScriptPubKeyMan& EnsureLegacyScriptPubKeyMan(CWallet& wallet, bool also_create)
{
    LegacyScriptPubKeyMan* spk_man = wallet.GetLegacyScriptPubKeyMan();
    if (!spk_man && also_create) {
        spk_man = wallet.GetOrCreateLegacyScriptPubKeyMan();
    }
    if (!spk_man) {
        throw JSONRPCError(RPC_WALLET_ERROR, "This type of wallet does not support this command");
    }
    return *spk_man;
}
static void WalletTxToJSON(interfaces::Chain& chain, const CWalletTx& wtx, UniValue& entry)