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. 
RemoveWatchOnly(script);
    }
    if (!m_storage.HasEncryptionKeys()) {
        return batch.WriteKey(pubkey,
                                                 secret.GetPrivKey(),
                                                 mapKeyMetadata[pubkey.GetID()]);
    }
    m_storage.UnsetBlankWalletFlag(batch);
    return true;
}
bool LegacyScriptPubKeyMan::LoadCScript(const CScript& redeemScript)
{
    /* A sanity check was added in pull #3843 to avoid adding redeemScripts
     * that never can be redeemed. However, old wallets may still contain
     * these. Do not add them to the wallet and warn. */
    if (redeemScript.size() > MAX_SCRIPT_ELEMENT_SIZE)
    {
        std::string strAddr = EncodeDestination(ScriptHash(redeemScript));
        WalletLogPrintf("%s: Warning: This wallet contains a redeemScript of size %i which exceeds maximum size %i thus can never be redeemed. Do not use address %s.\n", __func__, redeemScript.size(), MAX_SCRIPT_ELEMENT_SIZE, strAddr);
        return true;
    }
    return FillableSigningProvider::AddCScript(redeemScript);
}
void LegacyScriptPubKeyMan::LoadKeyMetadata(const CKeyID& keyID, const CKeyMetadata& meta)
{
    LOCK(cs_KeyStore);
    UpdateTimeFirstKey(meta.nCreateTime);
    mapKeyMetadata[keyID] = meta;
}
void LegacyScriptPubKeyMan::LoadScriptMetadata(const CScriptID& script_id, const CKeyMetadata& meta)