refactor: clarify diagnostics and adopt ptrcast inference

source/parser/parser.test.hon

@@ -30,7 +30,7 @@ parses_expression_precedence_through_tree_views test {
     try testing.expect_equal(ast.ExprKind.binary, ast.expr_kind(&tree, add.right))
     multiply :: ast.binary_expr(&tree, add.right)
     try testing.expect_equal(ast.BinaryOperator.multiply, multiply.operator)
-    try testing.expect_equal(0, diagnostics.len(&diagnostic_store))
+    try testing.expect_equal(0, diagnostics.count(&diagnostic_store))
 }
 
 parses_function_structure_through_tree_views test {
@@ -63,7 +63,7 @@ parses_function_structure_through_tree_views test {
     try testing.expect_equal(first.type, second.type)
     try testing.expect(first.type != third.type)
     try testing.expect_equal(1, ast.block_statement_count(&tree, function.body))
-    try testing.expect_equal(0, diagnostics.len(&diagnostic_store))
+    try testing.expect_equal(0, diagnostics.count(&diagnostic_store))
 }
 
 recovers_invalid_declaration_and_preserves_sibling test {