Update to latest prql-compiler

[aljazerzen]

No description provided.

[snth]

I need to look over these changes more and try them out. I know what I had was quite hacky but I think there was a reason for it.

[aljazerzen]

If I try to summarize, you had something like this:

prql_source
  .split_by_lines()
  .insert(
     1, "table source_name = (from a_name = a_key)"
  )
  .join('\n')
  .compile_prql()
  .replace('a_key', "read_csv('source_file.csv')")

I've changed it to:

let pl_stmts = parse(prql_source)
pl_stmts.insert(1, parse("let source_name = s'''read_csv('source_file.csv')'''"))
compile(pl_stmts)