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. 
void UnsetWalletFlagWithDB(WalletBatch& batch, uint64_t flag);
    
    void UnsetBlankWalletFlag(WalletBatch& batch) override;
    
    interfaces::Chain* m_chain;
    
    std::string m_name;
    
    std::unique_ptr<WalletDatabase> m_database;
    /**
     * The following is used to keep track of how far behind the wallet is
     * from the chain sync, and to allow clients to block on us being caught up.
     *
     * Processed hash is a pointer on node's tip and doesn't imply that the wallet
     * has scanned sequentially all blocks up to this one.
     */
    uint256 m_last_block_processed GUARDED_BY(cs_wallet);
    /** Height of last block processed is used by wallet to know depth of transactions
     * without relying on Chain interface beyond asynchronous updates. For safety, we
     * initialize it to -1. Height is a pointer on node's tip and doesn't imply
     * that the wallet has scanned sequentially all blocks up to this one.
     */
    int m_last_block_processed_height GUARDED_BY(cs_wallet) = -1;
    std::map<OutputType, ScriptPubKeyMan*> m_external_spk_managers;
    std::map<OutputType, ScriptPubKeyMan*> m_internal_spk_managers;
    
    
    std::map<uint256, std::unique_ptr<ScriptPubKeyMan>> m_spk_managers;
    /**
     * Catch wallet up to current chain, scanning new blocks, updating the best