Emergency stops: if a swap stalls on Avalanche, cancel pending tx, raise gas slightly, re-quote

https://wiki-velo.win/index.php/Gas_Tokens_and_Fee_Rebates:_Cheaper_Swaps_on_Avalanche

Emergency stops: if a swap stalls on Avalanche, cancel pending tx, raise gas slightly, re-quote, and retry with tighter parameters for success.