Use contract id in slot key (#321)

* Add BlockInfo#first_cons_time_of_current_block

Signed-off-by: Michael Tinker <michael.tinker@swirldslabs.com>

* Update SlotKey message to use ContractID instead of an int64, in order to be future-proof for sharding

Signed-off-by: Kim Rader <kim.rader@swirldslabs.com>

* Rename contract_number -> contractID

Signed-off-by: Kim Rader <kim.rader@swirldslabs.com>

---------

Signed-off-by: Michael Tinker <michael.tinker@swirldslabs.com>
Signed-off-by: Kim Rader <kim.rader@swirldslabs.com>
Co-authored-by: Michael Tinker <michael.tinker@swirldslabs.com>
Co-authored-by: Lev Povolotsky <lev@swirldslabs.com>

services/state/contract/storage_slot.proto

@@ -26,6 +26,8 @@ option java_package = "com.hederahashgraph.api.proto.java";
 // <<<pbj.java_package = "com.hedera.hapi.node.state.contract">>> This comment is special code for setting PBJ Compiler java package
 option java_multiple_files = true;
 
+import "basic_types.proto";
+
 /**
  * The key of a storage slot. A slot is scoped to a specific contract number.
  * 
@@ -35,7 +37,7 @@ message SlotKey {
     /**
      * The number of the contract whose storage this slot belongs to.
      */
-    int64 contract_number = 1;
+    ContractID contractID = 1;
 
     /**
      * The EVM key of this slot, when left-padded with zeros to form a 256-bit word.