parser debugging utilities + fixed paren sometimes producing unbalanced events

parser events now have a `from` field which has the source location of where the event was emitted.
this location is pretty-printed when using `Debug`

crates/haku/src/parser/tests.rs

@@ -18,7 +18,10 @@ fn parse(s: &str, f: fn(&mut Parser)) -> (Ast, NodeId) {
     f(&mut parser);
 
     if !parser.diagnostics.is_empty() {
-        panic!("parser emitted diagnostics: {:#?}", parser.diagnostics);
+        panic!(
+            "parser: {parser:#?}\nemitted diagnostics: {:#?}",
+            parser.diagnostics
+        );
     }
 
     let mut ast = Ast::new(1024);