[feature request] Split cache files into subfolders to reduce number of files in a single folder

**I'm submitting a feature request**

**Current behavior:**

Currently all outputs are stored into a single cache directory. On large projects and certain hardware this might have a negative impact on performances.

**Expected/desired behavior:**

Something that might remedy the situation is to write into subfolders that contain the first two characters of the key used for storing and use these for reading the cached output.