For eer make same gains with .mrc and .gain suffix (#700)

Needed due to relion's behaviour with eer using .mrc gain. In that case we want to use the .gain file, but if the collection is in tiff we need the .mrc file.

Author: stephen-riggs

src/murfey/server/gain.py

@@ -3,6 +3,7 @@
 import asyncio
 import logging
 import os
+import shutil
 from enum import Enum
 from pathlib import Path
 from typing import Dict, Tuple
@@ -130,4 +131,6 @@ async def prepare_eer_gain(
             f"{stderr.decode('utf-8').strip()}"
         )
         return None, None
+    # Also copy the gain as a .gain file
+    shutil.copy(secure_path(gain_path), secure_path(gain_out.with_suffix(".gain")))
     return gain_out, None