Update conditional argument handling to correctly support lambdas

[yjukaku]

Summary

This PR fixes the event condition call to check arity even when not using methods, since the user may have defined a condition using a lambda instead of a block. ie.

state :inside do
  event :exit, transitions_to: :outside, if: ->(obj) { dont_need_args(obj) }
end

Without this PR's change, this example raises an ArgumentError if you do something like obj.exit!(123), because the lambda is being called with 2 arguments when it expects 1.

Explanation

There are two types of Procs in Ruby, lambda-based procs and non-lambda (block-like) procs. They enforce arguments differently:

Block like

irb(main):001* proc_block = Proc.new do |a,b|
irb(main):002*   puts "a: #{a}, b: #{b}"
irb(main):003> end
=> #<Proc:0x000000012d315208 (irb):1>
irb(main):005> proc_block.call(1)
a: 1, b:
=> nil
irb(main):006> proc_block.call(1,2)
a: 1, b: 2
=> nil
irb(main):007> proc_block.call(1,2, 3)
a: 1, b: 2
=> nil

Lambda/stabby arrow

irb(main):004> proc_lambda = -> (a,b) { puts "a: #{a}, b: #{b}"  }
=> #<Proc:0x000000012cd39c80 (irb):4 (lambda)>
irb(main):008> proc_lambda.call(1)
(irb):4:in 'block in <top (required)>': wrong number of arguments (given 1, expected 2) (ArgumentError)
irb(main):009> proc_lambda.call(1,2)
a: 1, b: 2
=> nil
irb(main):010> proc_lambda.call(1,2,3)
(irb):4:in 'block in <top (required)>': wrong number of arguments (given 3, expected 2) (ArgumentError)

Thus we should check arity when calling an event's condition method or block/proc/lambda.

[yjukaku]

@geekq review please :)

I also have another PR incoming for the condition kwarg issue I tagged you in yesterday

[yjukaku]

Ping

[geekq]

Merged this PR first. The #247 will require a rebase