fix Last-Modified mtime overwriting post processor mtime (#7529)

https://github.com/mikf/gallery-dl/issues/7529#issuecomment-2989955455

- split '_mtime' into '_mtime_http' and '_mtime_meta'
- add PathFormat.set_mtime() method

gallery_dl/postprocessor/metadata.py

@@ -139,9 +139,7 @@ class MetadataPP(PostProcessor):
             archive.add(pathfmt.kwdict)
 
         if self.mtime:
-            mtime = pathfmt.kwdict.get("_mtime")
-            if mtime:
-                util.set_mtime(path, mtime)
+            pathfmt.set_mtime(path)
 
     def _run_stdout(self, pathfmt):
         self.write(sys.stdout, pathfmt.kwdict)

gallery_dl/postprocessor/mtime.py

@@ -36,7 +36,7 @@ class MtimePP(PostProcessor):
         if mtime is None:
             return
 
-        pathfmt.kwdict["_mtime"] = (
+        pathfmt.kwdict["_mtime_meta"] = (
             util.datetime_to_timestamp(mtime)
             if isinstance(mtime, datetime) else
             text.parse_int(mtime)

gallery_dl/postprocessor/ugoira.py

@@ -236,9 +236,7 @@ class UgoiraPP(PostProcessor):
             pathfmt.realpath = pathfmt.temppath
         else:
             if self.mtime:
-                mtime = pathfmt.kwdict.get("_mtime")
-                if mtime:
-                    util.set_mtime(pathfmt.realpath, mtime)
+                pathfmt.set_mtime()
             return True
 
     def convert_to_archive(self, pathfmt, tempdir):