fix: user's cursor can be offset for autocompletion

[juleswritescode]

Suppose we have an incomplete query and the user's cursor is too far off:

select * from {}

In that case, we couldn't walk the tree-sitter tree.
When we tried to go to the child node at the cursor position, tree-sitter would stay on the PROGRAM node (every tree's head) which lead to unexpected contexts and infinite recursion.

That's now fixed! We simply "move the cursor" to the previous node:

select * from {} becomes select * from{}.

Note: Treesitter is already able to deal with {} select * from.

Some additional stuff:

• added a tree-print script to the justfile (that's much cooler than Makefile, btw)
• adjusted and used some test-helpers, adjusted the tree_print binary to ignore newlines

[psteinroe]

great work!!