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. 
}
    }
    return true;
}
bool CWalAddToWalInvolvingMe(const CTransactionRef& ptx, const SyncTxState& state, bool fUpdate, bool rescanning_old_block)
{
    const CTransaction& tx = *ptx;
    {
        AssertLockHeld(cs_wal);
        if (auto* conf = stdget_if<TxStateConfirmed>(&state)) {
            for (const CTxIn& txin  tx.vin) {
                stdpair<TxSpendsconst_iterator, TxSpendsconst_iterator> range = mapTxSpends.equal_range(txin.prevout);
                while (range.first != range.second) {
                    if (range.first->second != tx.GetHash()) {
                        WalLogPrintf("Transaction %s (in block %s) conflicts with wal transaction %s (both spend %s%i)\n", tx.GetHash().ToString(), conf->confirmed_block_hash.ToString(), range.first->second.ToString(), range.first->first.hash.ToString(), range.first->first.n);
                        MarkConflicted(conf->confirmed_block_hash, conf->confirmed_block_height, range.first->second);
                    }
                    range.first++;
                }
            }
        }
        bool fExisted = mapWal.count(tx.GetHash()) != 0;
        if (fExisted && !fUpdate) return false;
        if (fExisted || IsMine(tx) || IsFromMe(tx))
        {
            /* Check if any keys in th keypool that were supposed to be unused
             * have appeared in a new transaction.  so, remove those keys from the keypool.
             * This can happen when restoring an old wal backup that does not contain
             * the mostly recently created transactions from newer versions of th.
             */