Avoid Array instances when normalizing Arrays / Hashes

`each_with_object` allocates an array for each kv pair. Switching to
the slightly more verbose but less allocatey `each_pair` eliminates
array allocations.

This follows the similar change in Rails:
960de47f0e

lib/rackstash/fields/abstract_collection.rb

@@ -114,8 +114,9 @@ module Rackstash
         when Rackstash::Fields::Hash, Rackstash::Fields::Array
           return wrap ? value : value.raw
         when ::Hash
-          hash = value.each_with_object(Concurrent::Hash.new) do |(k, v), memo|
+          hash = Concurrent::Hash.new
-            memo[utf8_encode(k)] = normalize(v, scope: scope)
+          value.each_pair do |k, v|
+            hash[utf8_encode(k)] = normalize(v, scope: scope)
           end
           if wrap
             hash = Rackstash::Fields::Hash.new.tap do |hash_field|
@@ -124,8 +125,9 @@ module Rackstash
           end
           return hash
         when ::Array, ::Set, ::Enumerator
-          array = value.each_with_object(Concurrent::Array.new) do |e, memo|
+          array = Concurrent::Array.new
-            memo << normalize(e, scope: scope)
+          value.each do |e|
+            array << normalize(e, scope: scope)
           end
           if wrap
             array = Rackstash::Fields::Array.new.tap do |array_field|

spec/rackstash/fields/abstract_collection_spec.rb

@@ -224,6 +224,11 @@ describe Rackstash::Fields::AbstractCollection do
         expect(normalize(hash, wrap: false).keys).to all be_frozen
       end
 
+      it 'returns a Concurrent::Hash with wrap: false' do
+        hash = { 'one' => 1 }
+        expect(normalize(hash, wrap: false)).to be_an_instance_of(Concurrent::Hash)
+      end
+
       it 'normalizes all values' do
         hash = { 'key' => :beepboop }
 
@@ -288,6 +293,11 @@ describe Rackstash::Fields::AbstractCollection do
         expect(normalize(array, wrap: false)).to all be_frozen
       end
 
+      it 'returns a Concurrent::Array with wrap: false' do
+        array = [1, :two, 'three']
+        expect(normalize(array, wrap: false)).to be_an_instance_of(Concurrent::Array)
+      end
+
       it 'normalizes all values' do
         array = ['boop', :beep]