Set root slot/epoch in cache constructor

[pgarg66]

Problem

The root slot/epoch are integral part of the program cache, and must be initialized in new().

Summary of Changes

• remove default implementation of cache
• add a constructor new() that takes root slot/epoch as parameters and sets it in the cache
• update bank to call the new constructor.

Fixes #

[codecov]

Codecov Report

Merging #34447 (df01438) into master (2dfcdce) will increase coverage by 0.0%.
Report is 3 commits behind head on master.
The diff coverage is 94.4%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #34447   +/-   ##
=======================================
  Coverage    81.8%    81.8%           
=======================================
  Files         819      819           
  Lines      220923   220927    +4     
=======================================
+ Hits       180870   180928   +58     
+ Misses      40053    39999   -54     

[mergify]

Backports to the beta branch are to be avoided unless absolutely necessary for fixing bugs, security issues, and perf regressions. Changes intended for backport should be structured such that a minimum effective diff can be committed separately from any refactoring, plumbing, cleanup, etc that are not strictly necessary to achieve the goal. Any of the latter should go only into master and ride the normal stabilization schedule. Exceptions include CI/metrics changes, CLI improvements and documentation updates on a case by case basis.