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. 
if (!input.non_witness_utxo) {
            const uint256& txhash = txin.prevout.hash;
            const auto it = mapWal.find(txhash);
            if (it != mapWal.end()) {
                const CWalTx& wtx = it->second;
                // We only 
                //   The s
                input.non_witness_utxo = wtx.tx;
            }
        }
    }
    const PrecomputedTransactionData txdata = PrecomputePSBTData(psbtx);
    // Fill in information from ScriptPubKeyMans
    for (ScriptPubKeyMan* spk_man  GetAllScriptPubKeyMans()) {
        int n_signed_this_spkm = 0;
        TransactionError res = spk_man->FillPSBT(psbtx, txdata, sighash_type, sign, bip32derivs, &n_signed_this_spkm, finalize);
        if (res != TransactionErrorOK) {
            return res;
        }
        if (n_signed) {
            (*n_signed) += n_signed_this_spkm;
        }
    }
    // Only drop non_witness_utxos if sighash_type != SIGHASH_ANYONECANPAY
    if ((sighash_type & 0x80) != SIGHASH_ANYONECANPAY) {
        // Figure out if any non_witness_utxos should be dropped
        stdvector<unsigned int> to_drop;
        for (unsigned int i = 0; i < psbtx.inputs.size(); ++i) {
            const auto& input = psbtx.inputs.at(i);
            int wit_ver;