Prevent setting to invalid state with update methods

[pangdaxing23]

I see there was some discussion about this issue in #49 , but it seems the validations did not make it into the master branch.

# job.rb
class Job < ApplicationRecord
  enum :status, {pending: 0, running: 1, done: 2, cancelled: 3} do
    event :run do
      transition [:pending] => :running
    end

    event :cancel do
      transition [:pending, :running] => :cancelled
    end

    event :finish do
      transition [:running] => :done
    end
  end
end

irb(main):001> job = Job.create!
=> #<Job:0x0000000107822e60 id: 1, status: "pending", created_at: Sun, 22 Sep 2024 15:35:34.179823000 UTC +00:00, updated_at: Sun, 22 Sep 2024 15:35:34.179823000 UTC +00:00>
irb(main):002> job.run!
=> true
irb(main):003> job.status
=> "running"
irb(main):004> job.finish!
=> true
irb(main):005> job.status
=> "done"
irb(main):006> job.cancel!
GEMPATH/stateful_enum-0.7.0/lib/stateful_enum/machine.rb:71:in `block (2 levels) in initialize': Invalid transition (RuntimeError)
irb(main):007> job.update status: :cancelled
=> true
irb(main):008> job.status
=> "cancelled"