Add portable persistent Raw preload cache

Author: bruAristimunha

doc/changes/dev/14216.newfeature.rst

@@ -0,0 +1,2 @@
+Speed up repeated preloading of uncompressed FIF, EDF/BDF, and BrainVision
+recordings with a persistent copy-on-write decoded-data cache, by `Bruno Aristimunha`_.

mne/channels/channels.py

@@ -748,6 +748,7 @@ def add_channels(self, add_list, force_update_info=False):
         # Now update the attributes
         if (
             isinstance(self._data, np.memmap)
+            and self._data.mode != "c"
             and con_axis == 0
             and sys.platform != "darwin"
         ):  # resizing not available--no mremap