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. 
boost::signals2::signal<void (bool fHaveWatchOnly)> NotifyWatchonlyChanged;
    
    boost::signals2::signal<void ()> NotifyCanGetAddressesChanged;
    /**
     * Wallet status (encrypted, locked) changed.
     * Note: Called without locks held.
     */
    boost::signals2::signal<void (CWallet* wallet)> NotifyStatusChanged;
    
    bool GetBroadcastTransactions() const { return fBroadcastTransactions; }
    
    void SetBroadcastTransactions(bool broadcast) { fBroadcastTransactions = broadcast; }
    
    bool TransactionCanBeAbandoned(const uint256& hashTx) const;
    
    bool AbandonTransaction(const uint256& hashTx);
    
    bool MarkReplaced(const uint256& originalHash, const uint256& newHash);
    
    static std::shared_ptr<CWallet> Create(WalletContext& context, const std::string& name, std::unique_ptr<WalletDatabase> database, uint64_t wallet_creation_flags, bilingual_str& error, std::vector<bilingual_str>& warnings);
    /**
     * Wallet post-init setup
     * Gives the wallet a chance to register repetitive tasks and complete post-init tasks
     */
    void postInitProcess();
    bool BackupWallet(const std::string& strDest) const;
    
    bool IsHDEnabled() const;
    
    bool CanGetAddresses(bool internal = false) const;