Since #13666 our fee calculation assumes that ECSDA signatures are a maximum of 71 bytes, rather than 72. However, not all hardware wallets implement R-value grinding.

This can cause us to underpay fees when using an external signer. That's especially problematic when the user picks 1 sat/vbyte as the fee, because it won't even get into our own mempool.

The easiest solution would be to modify `ExternalSignerScriptPubKeyMan` to assume 72 bytes for ECSDA signatures.

Slightly more advanced would be to expand HWI to keep track of which devices and firmware versions (if any) support R-value grinding. We'd then have to store that in the wallet in some new field. Personally I'd rather work on better Taproot support, which thanks to Schnorr avoids this issue altogether. 
{
    CMutableTransaction txn;
    txn.vin.push_back(CTxIn(outpoint));
    if (!provider || !DummySignInput(*provider, txn.vin[0], txout, coin_control)) {
        return -1;
    }
    return GetVirtualTransactionInputSize(txn.vin[0]);
}
int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, const CCoinControl* coin_control)
{
    const std::unique_ptr<SigningProvider> provider = wallet->GetSolvingProvider(txout.scriptPubKey);
    return CalculateMaximumSignedInputSize(txout, COutPoint(), provider.get(), coin_control);
}
TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts, const CCoinControl* coin_control)
{
    CMutableTransaction txNew(tx);
    if (!wallet->DummySignTx(txNew, txouts, coin_control)) {
        return TxSize{-1, -1};
    }
    CTransaction ctx(txNew);
    int64_t vsize = GetVirtualTransactionSize(ctx);
    int64_t weight = GetTransactionWeight(ctx);
    return TxSize{vsize, weight};
}
TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const CCoinControl* coin_control)