revlog: minor refactor in the chunk gather process

revlog: minor refactor in the chunk gather process

We will introduce some caching in this method in the next changeset, we make
some of the most "disruptive" change first as touching this could break (and
maybe did during the development process).

--- a/mercurial/revlog.py	Tue Oct 24 11:08:49 2023 +0200
+++ b/mercurial/revlog.py	Fri Oct 27 02:57:09 2023 +0200
@@ -901,6 +901,8 @@
 
         l = []
         ladd = l.append
+        chunks = []
+        ladd = chunks.append
 
         if not self.data_config.with_sparse_read:
             slicedchunks = (revs,)
@@ -923,7 +925,8 @@
             except OverflowError:
                 # issue4215 - we can't cache a run of chunks greater than
                 # 2G on Windows
-                return [self._chunk(rev) for rev in revschunk]
+                for rev in revschunk:
+                    ladd((rev, self._chunk(rev)))
 
             decomp = self.decompress
             # self._decompressor might be None, but will not be used in that case
@@ -936,17 +939,18 @@
                 comp_mode = self.index[rev][10]
                 c = buffer(data, chunkstart - offset, chunklength)
                 if comp_mode == COMP_MODE_PLAIN:
-                    ladd(c)
+                    c = c
                 elif comp_mode == COMP_MODE_INLINE:
-                    ladd(decomp(c))
+                    c = decomp(c)
                 elif comp_mode == COMP_MODE_DEFAULT:
-                    ladd(def_decomp(c))
+                    c = def_decomp(c)
                 else:
                     msg = b'unknown compression mode %d'
                     msg %= comp_mode
                     raise error.RevlogError(msg)
-
-        return l
+                ladd((rev, c))
+
+        return [x[1] for x in chunks]
 
     def raw_text(self, node, rev):
         """return the possibly unvalidated rawtext for a revision