在首次 mint 时, 会有一个 1000 wei 的 lp 发送到了 address(0)上. 文档原文: To ameliorate rounding errors and increase the theoretical minimum tick size for liquidity provision, pairs burn the first [MINIMUM_LIQUIDITY](https://docs.uniswap.org/protocol/V2/reference/smart-contracts/pair#minimum_liquidity) pool tokens. For the vast majority of pairs, this will represent a trivial value. The burning happens automatically during the first liquidity provision, after which point the [totalSupply](https://docs.uniswap.org/protocol/V2/reference/smart-contracts/pair-erc-20#totalsupply) is forevermore bounded. token0: Token1 是按地址大小顺序排列的.