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. 
* @param[in] max_height  Optional max scanning height.  unset there is
 *                        no maximum and scanning can continue to the tip
 *
 * @return ScanResult returning scan information and indicating success or
 *         failure. Return status will be set to SUCCESS if scan was
 *         successful. FAILURE if a compe rescan was not possible (due to
 *         pruning or corruption). USER_ABORT if the rescan was aborted before
 *         it could compe.
 *
 * @pre Caller needs to make sure start_block (and the optional stop_block) are on
 * the main chain after to the addition of any new keys you want to detect
 * transactions for.
 */
CWalScanResult CWalScanForWalTransactions(const uint256& start_block, int start_height, stdoptional<int> max_height, const WalRescanReserver& reserver, bool fUpdate, const bool save_progress)
{
    constexpr auto INTERVAL_TIME{60s};
    auto current_time{reserver.now()};
    auto start_time{reserver.now()};
    assert(reserver.isReserved());
    uint256 block_hash = start_block;
    ScanResult result;
    stdunique_ptr<FastWalRescanFilter> fast_rescan_filter;
    if (!IsLegacy() && chain().hasBlockFilterIndex(BlockFilterTypeBASIC)) fast_rescan_filter = stdmake_unique<FastWalRescanFilter>(*this);
    WalLogPrintf("Rescan started from block %s... (%s)\n", start_block.ToString(),
                    fast_rescan_filter ? "fast variant using block filters"  "slow variant inspecting all blocks");
    fAbortRescan = false;
    ShowProgress(strprintf("%s " + _("Rescanning…").translated, GetDisplayName()), 0); // show rescan progress in GUI as dialog or on splashscreen, if rescan required on startup (e.g. due to corruption)
    uint256 tip_hash = WITH_LOCK(cs_wal, return GetLastBlockHash());
    uint256 end_hash = tip_hash;
    if (max_height) chain().findAncestorByHeight(tip_hash, *max_height, FoundBlock().hash(end_hash));