store: cache the `files()` return for store entries

This make it more efficient to directly use the entries list to retrieve data
in various location. It also make the entry record the file size it previously
promissed to user code, especially the stream clone code.

mercurial/store.py

@@ -475,6 +475,7 b' class SimpleStoreEntry(BaseStoreEntry):'
     _entry_path = attr.ib()
     _is_volatile = attr.ib(default=False)
     _file_size = attr.ib(default=None)
+    _files = attr.ib(default=None)
 
     def __init__(
         self,
@@ -486,15 +487,18 b' class SimpleStoreEntry(BaseStoreEntry):'
         self._entry_path = entry_path
         self._is_volatile = is_volatile
         self._file_size = file_size
+        self._files = None
 
     def files(self):
-        return [
+        if self._files is None:
+            self._files = [
             StoreFile(
                 unencoded_path=self._entry_path,
                 file_size=self._file_size,
                 is_volatile=self._is_volatile,
             )
         ]
+        return self._files
 
 
 @attr.s(slots=True, init=False)
@@ -507,6 +511,7 b' class RevlogStoreEntry(BaseStoreEntry):'
     target_id = attr.ib(default=None)
     _path_prefix = attr.ib(default=None)
     _details = attr.ib(default=None)
+    _files = attr.ib(default=None)
 
     def __init__(
         self,
@@ -521,6 +526,7 b' class RevlogStoreEntry(BaseStoreEntry):'
         self._path_prefix = path_prefix
         assert b'.i' in details, (path_prefix, details)
         self._details = details
+        self._files = None
 
     @property
     def is_changelog(self):
@@ -539,12 +545,13 b' class RevlogStoreEntry(BaseStoreEntry):'
         return self._path_prefix + b'.i'
 
     def files(self):
-        files = []
+        if self._files is None:
+            self._files = []
         for ext in sorted(self._details, key=_ext_key):
             path = self._path_prefix + ext
             data = self._details[ext]
-            files.append(StoreFile(unencoded_path=path, **data))
-        return files
+                self._files.append(StoreFile(unencoded_path=path, **data))
+        return self._files
 
     def get_revlog_instance(self, repo):
         """Obtain a revlog instance from this store entry