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 (LEGACY_OUTPUT_TYPES.count(type) == 0) {
        return util::Error{_("Error: Legacy wallets only support the \"legacy\", \"p2sh-segwit\", and \"bech32\" address types")};
    }
    assert(type != OutputType::BECH32M);
    
    TopUp();
    LOCK(cs_KeyStore);
    
    CPubKey new_key;
    if (!GetKeyFromPool(new_key, type)) {
        return util::Error{_("Error: Keypool ran out, please call keypoolrefill first")};
    }
    LearnRelatedScripts(new_key, type);
    return GetDestinationForKey(new_key, type);
}
typedef std::vector<unsigned char> valtype;
namespace {
/**
 * This is an enum that tracks the execution context of a script, similar to
 * SigVersion in script/interpreter. It is separate however because we want to
 * distinguish between top-level scriptPubKey execution and P2SH redeemScript
 * execution (a distinction that has no impact on consensus rules).
 */
enum class IsMineSigVersion