Daylight Savings Time issue in `to_yaml` specs

[nehresma]

There is a daylight savings time error that gets triggered in the to_yaml specs.

The specs in spec/examples/to_yaml_spec.rb all create Schedules using a Ruby time object (Time.new). This object of course doesn't respond to time_zone method, so the time object gets serialized as just a time string that includes the zone offset, rather than as a hash that includes the timezone name (which is what adds DST rule support).

This is easy to see and trigger on the command line. America/Phoenix does not observe DST, but America/New_York does, and is currently in standard time:

$ date
Fri Dec 13 01:52:03 PM EST 2024
$ TZ=America/Phoenix rspec spec/examples/to_yaml_spec.rb:80
Run options: include {:locations=>{"./spec/examples/to_yaml_spec.rb"=>[80]}}
.

Finished in 0.16943 seconds (files took 0.10325 seconds to load)
1 example, 0 failures

$ TZ=America/New_York rspec spec/examples/to_yaml_spec.rb:80
Run options: include {:locations=>{"./spec/examples/to_yaml_spec.rb"=>[80]}}
F

Failures:

  1) IceCube::Schedule to_yaml should be able to make a round-trip to YAML with .day_of_year
     Failure/Error:
       expect(schedule2.first(10).map { |r| r.to_s })
         .to eq(schedule1.first(10).map { |r| r.to_s })
     
       expected: ["2025-04-10 13:52:10 -0400", "2025-07-19 13:52:10 -0400", "2026-04-10 13:52:10 -0400", "2026-07-19 1...52:10 -0400", "2028-07-18 13:52:10 -0400", "2029-04-10 13:52:10 -0400", "2029-07-19 13:52:10 -0400"]
            got: ["2025-04-10 13:52:10 -0500", "2025-07-19 13:52:10 -0500", "2026-04-10 13:52:10 -0500", "2026-07-19 1...52:10 -0500", "2028-07-18 13:52:10 -0500", "2029-04-10 13:52:10 -0500", "2029-07-19 13:52:10 -0500"]
     
       (compared using ==)
     # ./spec/examples/to_yaml_spec.rb:88:in `block (2 levels) in <module:IceCube>'
     # ./spec/spec_helper.rb:76:in `block (3 levels) in <top (required)>'
     # ./spec/spec_helper.rb:75:in `block (2 levels) in <top (required)>'

Finished in 0.19318 seconds (files took 0.11404 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./spec/examples/to_yaml_spec.rb:80 # IceCube::Schedule to_yaml should be able to make a round-trip to YAML with .day_of_year

The spec is already requiring activesupport/time, so I propose that we alter the to_yaml_spec.rb specs to use ActiveSupport::TimeWithZone times instead. This will make the specs stop failing half the year when they're run in local timezone that have DST rules.