fix: use yum-epel resource for auth_cas

[damacus]

Summary

• replace the removed yum-epel recipe include with the yum_epel custom resource
• keep Fedora exempt and preserve existing source-install defaults
• exercise the Rocky Linux 9 package-install path in ChefSpec and Kitchen

Closes #963.

Verification

• chef install Policyfile.rb
• cookstyle (104 files, no offenses)
• ChefSpec (257 examples, 0 failures)
• KITCHEN_LOCAL_YAML=kitchen.dokken.yml kitchen test mod-auth-cas-rockylinux-9 --destroy=always
• second converge: 0/147 resources updated; InSpec passed
• independent spec and quality review: passed with no findings

[github-actions]

Slowest examples

Top 10 slowest examples (3.57 seconds, 15.77% of total time)

Example	Description	Time in seconds
spec/resources/module_spec.rb:46	apache2_install mod_proxy with custom configuration Installs mod_proxy with custom configuration	0.65072
spec/resources/mod_spec.rb:203	apache2_install mod_fastcgi outputs template correctly	0.46646
spec/resources/mod_auth_cas_spec.rb:30	apache2_mod_auth_cas ubuntu is expected to enable apache2_module "auth_cas"	0.40974
spec/resources/mod_spec.rb:120	apache2_install mod_pagespeed Creates the cache directory	0.39334
spec/resources/config_spec.rb:23	apache2_config install config template from external Creates a template from the specified cookbook	0.36901
spec/libraries/package_helpers_spec.rb:73	#default_apache_pkg with SUSE family is expected to write log "apache2"	0.29364
spec/libraries/log_spec.rb:61	#default_access_log with Debian is expected to write log "access.log"	0.26051
spec/libraries/default_modules_spec.rb:15	#default_modules systemd redhat is expected to write log "status, alias, auth_basic, authn_core, authn_file, authz_core, authz_groupfile, authz_host, authz_user, autoindex, deflate, dir, env, mime, negotiation, setenvif, log_config, logio, unixd, systemd"	0.25197
spec/libraries/lib_dir_spec.rb:61	#lib_dir x86 suse is expected to write log "/usr/lib/apache2"	0.23904
spec/resources/default_site_spec.rb:22	apache2_install Enable the default site Creates the default site template	0.23865