Revisit layering and definition of struct clockcache_entry{}, and possibly of struct clockcache{} #273

This issue was raised and discussed during reviews of PR #230 . Currently we have the following structures defined in clockccahe.h and the status flags for clockcache_entry{}->status defined in clockcache.c file

• struct clockcache_entry{}
• struct clockcache{}

The former certainly should be relocated to the .c file, so that there is no risk of other modules diddling with this structure.

Investigate if it's possible to also define clockcache{} in the .c file and leave an opaque reference to in the .h file. This will entail some rework in the places where this structure is stack-allocated to go through malloc, and some things to be done differently to init v/s create this structure when needed. Figure out how much of this rework is possible for the 2nd structure.