refactor(mypy): Finish type hint the rql/ module

- Type hint all `parse` functions inside rql/
- Create a type alias to represent what's returned by `parse` functions above
- Update RQLSTChecker.check method signature:
  * node parameter should be a BaseNode	or any children	of BaseNode class
- Type hint `copy_uid_node` function
- Remove useless variable: pyparse = parse
- Format without any compromise
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