feat(c-bridge): support for protocol upgrade when calculating dr's resolution timestamp

Author: guidiaz

bridges/centralized-ethereum/src/actors/dr_reporter.rs

@@ -102,7 +102,7 @@ pub struct Report {
     /// Data Request's unique query id as known by the WitnetOracle contract
     pub dr_id: DrId,
     /// Timestamp at which the reported result was actually generated
-    pub dr_timestamp: u64,
+    pub dr_timestamp: i64,
     /// Hash of the Data Request Transaction in the Witnet blockchain
     pub dr_tx_hash: Hash,
     /// Hash of the Data Request Tally Transaction in the Witnet blockchain

bridges/centralized-ethereum/src/actors/dr_sender.rs

@@ -189,7 +189,7 @@ impl DrSender {
 
                         dr_reporter_msgs.push(Report {
                             dr_id,
-                            dr_timestamp: u64::from_ne_bytes(get_timestamp().to_ne_bytes()),
+                            dr_timestamp: i64::from_ne_bytes(get_timestamp().to_ne_bytes()),
                             dr_tx_hash: zero_hash,
                             dr_tally_tx_hash: zero_hash,
                             result,