Replace deprecated chunk module with inline IFF parser

The chunk module was deprecated in 3.11 and removed in 3.13.
Our usage was minimal (read name, size, data, skip padding),
so a small _read_iff_chunk() helper replaces it with no deps.

src/mudlib/zmachine/quetzal.py

@@ -12,14 +12,30 @@
 # root directory of this distribution.
 #
 
-# Woohoo!  Python has a module to parse IFF files, which is a generic
-# interchange format.  A Quetzal file is in fact a type of IFF file.
-import chunk
 import os
+import struct
 
 from . import bitfield, zstackmanager
 from .zlogging import log
 
+
+def _read_iff_chunk(f):
+    """Read one IFF chunk from a file-like object. Returns (name, data).
+
+    Raises EOFError when there are no more chunks to read.
+    """
+    header = f.read(8)
+    if len(header) < 8:
+        raise EOFError
+    name = header[:4]
+    (size,) = struct.unpack(">I", header[4:8])
+    data = f.read(size)
+    # IFF chunks are padded to even byte boundaries
+    if size % 2 == 1:
+        f.read(1)
+    return name, data
+
+
 # The general format of Queztal is that of a "FORM" IFF file, which is
 # a container class for 'chunks'.
 #
@@ -339,10 +355,8 @@ class QuetzalParser:
         log("Parsing chunks from byte data")
         try:
             while 1:
-                c = chunk.Chunk(self._file)
+                chunkname, chunk_data = _read_iff_chunk(self._file)
-                chunkname = c.getname()
+                chunksize = len(chunk_data)
-                chunksize = c.getsize()
-                chunk_data = c.read(chunksize)
                 log(f"** Found chunk ID {chunkname}: length {chunksize}")
                 self._last_loaded_metadata[chunkname] = chunksize
 
@@ -406,10 +420,8 @@ class QuetzalParser:
 
         try:
             while 1:
-                c = chunk.Chunk(self._file)
+                chunkname, data = _read_iff_chunk(self._file)
-                chunkname = c.getname()
+                chunksize = len(data)
-                chunksize = c.getsize()
-                data = c.read(chunksize)
                 log(f"** Found chunk ID {chunkname}: length {chunksize}")
                 self._last_loaded_metadata[chunkname] = chunksize