Add support for multi-test files

[msanchezdev]

Fixes: #11

The idea is to be able to specify multiple tests in a single file to reduce the number of files, and keep tests scoped.

In order to allow differentiating between tests a test identifier can be added like in the examples below.

Two linefeeds are enough to separate on test from the other. Considered adding a customizable separator but I'm not sure that's needed.

test_one: First test example
=======
fn x() int {
    return 1;
}
=======
(source_file
  (function_definition
    (identifier: "x")
    (parameter_list)
    (primitive_type: "int")
    (block
      (inner_block
        (return_statement
          (number: "1")
        )
      )
    )
  )
)


test_two: Second test example
=======
fn y() bool {
    return true;
}
=======
(source_file
  (function_definition
    (identifier: "y")
    (parameter_list)
    (primitive_type: "bool")
    (block
      (inner_block
        (return_statement
          (boolean: "true")
        )
      )
    )
  )
)

[jdidion]

Thanks! Looked like the build failed on some linter issues https://github.com/jdidion/pest-test/actions/runs/18766822128. Once these are fixed up it should be good to merge.