* feat(accumulator_updater): initial skeleton for accumulator_udpater program
Initial layout for accumulator updater program. Includes mock-cpi-caller which is meant to represent
pyth oracle(or any future allowed program) that will call the accumulator updater program. All
implementation details are open for discussion/subject to change
* test(accumulator_updater): add additional checks in tests and minor clean up
* chore(accumulator_updater): misc clean-up
* refactor(accumulator_updater): added comments & to-dos and minor refactoring to address PR comments
swimricky