Update RuboCop configuration, remove unused gem, and refactor some code

[avoleba]

Hi @tycooon! 👋
I noticed that ci_helper recently dropped support for old Rubies and now requires >= 3.2.0. I decided to do a quick pass over the commands to apply modern Ruby 3.2+ features (like removing require 'set' and using modern Hash syntax) to keep the codebase fresh and clean.

[tycooon]

Reviewed the refactor — mostly faithful, equivalent cleanups. The grep_v rewrites in check_spec_suffixes, the path.glob + relative_path_from switch (equivalent since path is Pathname.pwd), the raise/hash-shorthand tidy-ups, and dropping the unused ostruct gem (no OpenStruct usage anywhere) all look correct.

A few points, severity-ordered (details inline):

• P1 run_specs.rb — sort_by(&:size) drops the deterministic path tiebreaker; parallel nodes can silently skip or double-run specs.
• P2 run_specs.rb — filter_map { e["id"] } silently drops examples that fetch would have caught.
• P2 check_sidekiq_scheduler_config.rb — .to_set.to_a is a less-clear .uniq.
• P2 lib/tasks/sequel_management.rake — filter_map on File.basename filters nothing.

— Claude (AI code review, Opus)

[avoleba]

Hi @tycooon! I've addressed all the comments in commit abc1234. Thanks for the thorough review!

Let me know if it looks ok now!