Move parsing of hspec tree to parse_positions

[mrcjkb]

After having browsed the neotest sources a bit, I think the best way to solve this is a complete rework of how neotest-haskell parses positions and later constructs the test commands from the positions.

The current parse_positions implementation runs one big tree-sitter query that results in what is effectively a list of positions. And then build_spec runs queries on each position to build the hspec --match filters for each position.
This works well if there's only one position to run (the "nearest"), but not if there are more than one.

If I change parse_positions to run separate smaller tree-sitter queries and return a tree that is equivalent to the hspec tree (as far as is possible with the limited tree-sitter capabilities), neotest should only pass the respective parent nodes to build_spec.
For the entire file, this would likely be a single position, unless the Spec is constructed using multiple top-level functions.
Then I can construct the hspec --match filter in build_spec by simply iterating over each position's parent nodes.

It would still be nice to be able to merge multiple positions into a single command, but this will definitely need a patch to neotest.

Originally posted by @mrcjkb in #45 (comment)