fix: add require 'ostruct' for Ruby 3.2+ compatibility

[damacus]

Ruby 3.2+ no longer auto-loads OpenStruct. The spec_helper uses OpenStruct for test doubles but was missing the explicit require, causing all 19 library specs to fail.

[github-actions]

Slowest examples

Top 10 slowest examples (0.58 seconds, 46.6% of total time)

Example	Description	Time in seconds
spec/recipes/default_spec.rb:10	ark::default does not install the gcc-c++ package	0.09213
spec/recipes/default_spec.rb:6	ark::default installs core packages	0.064
spec/recipes/default_spec.rb:14	ark::default is expected not to install seven_zip_tool "ark"	0.06397
spec/recipes/default_spec.rb:23	ark::default sets default attributes prefix root	0.06021
spec/recipes/default_spec.rb:19	ark::default sets default attributes apache mirror	0.05971
spec/recipes/default_spec.rb:27	ark::default sets default attributes prefix bin	0.05764
spec/recipes/default_spec.rb:31	ark::default sets default attributes prefix home	0.05703
spec/recipes/centos/default_spec.rb:8	ark::default installs core packages	0.04627
spec/resources/default_spec.rb:190	ark dump dumps	0.0453
spec/resources/default_spec.rb:316	ark install_with_make installs with make	0.03874