Add mutations for getting items from arrays.

In particular, to avoid sampling (introducing nondeterminism) when first/last will do.

lib/mutant/mutator/node/send.rb

@@ -18,6 +18,8 @@ module Mutant
           reverse_each:  %i[each],
           reverse_merge: %i[merge],
           map:           %i[each],
+          sample:        %i[first last],
+          first:         %i[last],
           send:          %i[public_send __send__],
           __send__:      %i[public_send],
           method:        %i[public_method],

meta/send.rb

@@ -657,3 +657,18 @@ Mutant::Meta::Example.add :send do
   mutation '!a.eql?(b)'
   mutation '!a.equal?(b)'
 end
+
+Mutant::Meta::Example.add :send do
+  source 'sample'
+
+  singleton_mutations
+  mutation 'first'
+  mutation 'last'
+end
+
+Mutant::Meta::Example.add :send do
+  source 'first'
+
+  singleton_mutations
+  mutation 'last'
+end