fix: preserve fn newline metadata after semicolons (#112)

Capture newline metadata for anonymous functions when the separator is a
semicolon token that carries newline count.

This aligns cases like `fn ;\n -> :ok end` with Elixir metadata while
avoiding incorrect `newlines: 0` for same-line semicolons.

Adds deterministic regression assertions in the property-regression test
block.

---------

Co-authored-by: Mitchell Hanberg <mitch@mitchellhanberg.com>

Author: mkaput

lib/spitfire.ex

@@ -2110,7 +2110,18 @@ defmodule Spitfire do
     trace "parse_anon_function", trace_meta(parser) do
       meta = current_meta(parser)
 
-      newlines = get_newlines(parser)
+      semicolon_newlines =
+        case peek_newlines(parser, :";") do
+          nl when is_integer(nl) and nl > 0 -> nl
+          _ -> nil
+        end
+
+      newlines =
+        case peek_newlines(parser) || semicolon_newlines do
+          nil -> []
+          nl -> [newlines: nl]
+        end
+
       parser = parser |> next_token() |> eat_eoe()
 
       # fn creates its own stab scope

test/spitfire_test.exs

@@ -2297,6 +2297,10 @@ defmodule SpitfireTest do
       # In-match operator (<-) in map keys - should be part of key, not wrap it
       assert Spitfire.parse("%{s\\\\r => 1}") == s2q("%{s\\\\r => 1}")
 
+      # Fn args with semicolon/newline trivia
+      assert Spitfire.parse("fn ;\n -> :ok end") == s2q("fn ;\n -> :ok end")
+      assert Spitfire.parse("fn ; -> :ok end") == s2q("fn ; -> :ok end")
+
       # Struct type with dot-call target
       assert Spitfire.parse("%e.(){}") == s2q("%e.(){}")
       assert Spitfire.parse("%e.(1){}") == s2q("%e.(1){}")