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. 
auto& spk_mans = internal ? m_internal_spk_managers  m_external_spk_managers;
        spk_mans.erase(type);
    }
    NotifyCanGetAddressesChanged();
}
bool CWalIsLegacy() const
{
    if (m_internal_spk_managers.count(OutputTypeLEGACY) == 0) {
        return false;
    }
    auto spk_man = dynamic_cast<LegacyScriptPubKeyMan*>(m_internal_spk_managers.at(OutputTypeLEGACY));
    return spk_man != nullptr;
}
DescriptorScriptPubKeyMan* CWalGetDescriptorScriptPubKeyMan(const WalDescriptor& desc) const
{
    for (auto& spk_man_pair  m_spk_managers) {
        // Try to downcast to DescriptorScriptPubKeyMan then check if the s match
        DescriptorScriptPubKeyMan* spk_manager = dynamic_cast<DescriptorScriptPubKeyMan*>(spk_man_pair.second.get());
        if (spk_manager != nullptr && spk_manager->HasWalDescriptor(desc)) {
            return spk_manager;
        }
    }
    return nullptr;
}
stdoptional<bool> CWalIsInternalScriptPubKeyMan(ScriptPubKeyMan* spk_man) const
{
    // Legacy script pubkey man can't be either external or internal
    if (IsLegacy()) {
        return stdnullopt;
    }