Review usages of Integer#size in the gem

[eregon]

From @XrXr in https://bugs.ruby-lang.org/issues/20614#note-8, we should review usages of Integer#size as it is not equal to pointer size on Windows.

[eregon]

https://github.com/search?q=repo%3Aruby-concurrency%2Fconcurrent-ruby%200.size&type=code

concurrent-ruby/lib/concurrent-ruby/concurrent/thread_safe/util.rb

Line 10 in cadc8de

FIXNUM_BIT_SIZE = (0.size * 8) - 2

concurrent-ruby/lib/concurrent-ruby/concurrent/utility/native_integer.rb

Lines 7 to 8 in cadc8de

	MIN_VALUE = -(2**(0.size * 8 - 2))
	MAX_VALUE = (2**(0.size * 8 - 2) - 1)

concurrent-ruby/lib/concurrent-ruby/concurrent/thread_safe/util/xor_shift_random.rb

Line 32 in cadc8de

if 0.size == 4