(CONT-173) - Updating deprecated facter instances

(CONT-173) - Updating deprecated facter instances
Prior to this PR, this module contained instances of Facter::Util::Resolution.exec and Facter::Util::Resolution.which, which are deprecated.
This PR aims to replace these exec helpers with their supported Facter::Core::Execution counterparts.

This PR:
- Replaced all Facter::Util::Resolution instances with corresponding Facter::Core::Execution exec helpers

Fix rubucop linting error

This commit corrects an error identified by rubocop in spec testing.