Feature/file storage: Append, Fetch, Delete, Modify Rows

[tom6311tom6311]

Brief

• Implement file storage features of append, fetch, delete, modify rows

Features:

1. Functions for row-level operations:
   • File::append_rows, File::fetch_rows, File::delete_rows, File::modify_rows
2. Design test cases for the 4 functionalities
3. Remove __rid__ attribute for each stored row.
4. Implement the __valid__ attribute for each stored row, which indicates if the row has been deleted.
5. Rename TableInfo to TableMeta
6. Simplify the error-expected test cases by using Result.unwrap_err()

Known Issues:

1. Currently, most of row operations require read/write over whole TSV file, which is very inefficient. This can be solved by further binary file implementations.