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. 
{
    LOCK(cs_desc_man);
    m_wallet_descriptor.cache = cache;
    for (int32_t i = m_wallet_descriptor.range_start; i < m_wallet_descriptor.range_end; ++i) {
        FlatSigningProvider out_keys;
        std::vector<CScript> scripts_temp;
        if (!m_wallet_descriptor.descriptor->ExpandFromCache(i, m_wallet_descriptor.cache, scripts_temp, out_keys)) {
            throw std::runtime_error("Error: Unable to expand wallet descriptor from cache");
        }
        
        for (const CScript& script : scripts_temp) {
            if (m_map_script_pub_keys.count(script) != 0) {
                throw std::runtime_error(strprintf("Error: Already loaded script at index %d as being at index %d", i, m_map_script_pub_keys[script]));
            }
            m_map_script_pub_keys[script] = i;
        }
        for (const auto& pk_pair : out_keys.pubkeys) {
            const CPubKey& pubkey = pk_pair.second;
            if (m_map_pubkeys.count(pubkey) != 0) {
                
                
                continue;
            }
            m_map_pubkeys[pubkey] = i;
        }
        m_max_cached_index++;
    }
}
bool DescriptorScriptPubKeyMan::AddKey(const CKeyID& key_id, const CKey& key)