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. 
std::unique_ptr<interfaces::Handler> HandleLoadWallet(WalletContext& context, LoadWalletFn load_wallet);
void NotifyWalletLoaded(WalletContext& context, const std::shared_ptr<CWallet>& wallet);
std::unique_ptr<WalletDatabase> MakeWalletDatabase(const std::string& name, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error);
constexpr CAmount DEFAULT_PAY_TX_FEE = 0;
static const CAmount DEFAULT_FALLBACK_FEE = 0;
static const CAmount DEFAULT_DISCARD_FEE = 10000;
static const CAmount DEFAULT_TRANSACTION_MINFEE = 1000;
static const CAmount DEFAULT_CONSOLIDATE_FEERATE{10000}; 
/**
 * maximum fee increase allowed to do partial spend avoidance, even for nodes with this feature disabled by default
 *
 * A value of -1 disables this feature completely.
 * A value of 0 (current default) means to attempt to do partial spend avoidance, and use its results if the fees remain *unchanged*
 * A value > 0 means to do partial spend avoidance if the fee difference against a regular coin selection instance is in the range [0..value].
 */
static const CAmount DEFAULT_MAX_AVOIDPARTIALSPEND_FEE = 0;
constexpr CAmount HIGH_APS_FEE{COIN / 10000};
static const CAmount WALLET_INCREMENTAL_RELAY_FEE = 5000;
static const bool DEFAULT_SPEND_ZEROCONF_CHANGE = true;
static const bool DEFAULT_WALLET_REJECT_LONG_CHAINS{true};
static const unsigned int DEFAULT_TX_CONFIRM_TARGET = 6;
static const bool DEFAULT_WALLET_RBF = true;
static const bool DEFAULT_WALLETBROADCAST = true;
static const bool DEFAULT_DISABLE_WALLET = false;
static const bool DEFAULT_WALLETCROSSCHAIN = false;
constexpr CAmount DEFAULT_TRANSACTION_MAXFEE{COIN / 10};
constexpr CAmount HIGH_TX_FEE_PER_KB{COIN / 100};
constexpr CAmount HIGH_MAX_TX_FEE{100 * HIGH_TX_FEE_PER_KB};
static constexpr size_t DUMMY_NESTED_P2WPKH_INPUT_SIZE = 91;
class CCoinControl;