Adjust request protocol/ Check file base path

[Dong513]

Request format

• case0: init (must be the first request in each connection)
  • username||||||key
• case1: normal
  • username||dbname||command;
• case2: user without a database
  • username||||create database dbname;

[todo[bot]]

save key

https://github.com/tigercosmos/StellarSQL/blob/b1872d18deae5ed29d78595ea8c83fa9400a8999/src/connection/request.rs#L65-L70

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This comment was generated by todo based on a TODO comment in b1872d18deae5ed29d78595ea8c83fa9400a8999 in #13. cc @Dong513.