fix: Reduce Hash Allocations in PG Instrumentation (#232)

* chore: enable Style/CollectionCompact

* chore: Minimize object allocation

This change removes allocation of 2 additional hashes per PG SQL span.

.rubocop.yml

@@ -55,5 +55,3 @@ Layout/LineLength:
   Max: 250
 Lint/RedundantRequireStatement:
   Enabled: false
-Style/CollectionCompact:
-  Enabled: false

instrumentation/pg/lib/opentelemetry/instrumentation/pg/patches/connection.rb

@@ -86,7 +86,7 @@ def span_attrs(kind, *args)
             attrs = { 'db.operation' => validated_operation(operation), 'db.postgresql.prepared_statement_name' => statement_name }
             attrs['db.statement'] = sql unless config[:db_statement] == :omit
             attrs.merge!(OpenTelemetry::Instrumentation::PG.attributes)
-            attrs.reject! { |_, v| v.nil? }
+            attrs.compact!
 
             [span_name(operation), client_attributes.merge(attrs)]
           end
@@ -131,7 +131,9 @@ def client_attributes
             }
             attributes['peer.service'] = config[:peer_service] if config[:peer_service]
 
-            attributes.merge(transport_attrs).reject { |_, v| v.nil? }
+            attributes.merge!(transport_attrs)
+            attributes.compact!
+            attributes
           end
 
           def transport_addr