Add PersistedState#instant

See openhab/openhab-core#4384

Signed-off-by: Jimmy Tanagra <jcode@tanagra.id.au>

lib/openhab/core/items/persistence.rb

@@ -88,10 +88,14 @@ class PersistedState < SimpleDelegator
           # @!attribute [r] timestamp
           # @return [ZonedDateTime]
 
+          # @!attribute [r] instant
+          # @return [Instant] The timestamp as an Instant
+          # @since openHAB 4.3
+
           # @!attribute [r] name
           # @return [String] Item name
 
-          delegate %i[timestamp name] => :@historic_item
+          delegate %i[timestamp instant name] => :@historic_item
 
           def initialize(historic_item, state = nil)
             @historic_item = historic_item

spec/openhab/core/items/persistence_spec.rb

@@ -189,6 +189,10 @@ def initialize(timestamp, state, name)
       expect(max).to be_a described_class::PersistedState
       expect(max).to eql max.state
       expect(max.timestamp).to be_a ZonedDateTime
+      # @deprecated OH 4.2 - Remove if guard when dropping oh 4.2 support
+      if OpenHAB::Core.version >= OpenHAB::Core::V4_3 && described_class::PersistedState.instance_methods.include?(:instant)
+        expect(max.instant).to be_a Instant
+      end
     end
 
     it "is inspectable" do