client: Use single time variable when handling heartbeat response. (#26238)

When the client handles an update status response from the server,
it modifies its heartbeat stop tracker with a time set once the
RPC call returns. It optionally also emits a log message, if the
client suspects it has missed a heartbeat.

These times were originally tracked by two different calls to the
time function which were executed 2 microseconds apart. There is
no reason we cannot use a single time variable for both uses which
saves us one whole call to time.Now.

client/client.go

@@ -2145,7 +2145,7 @@ func (c *Client) updateNodeStatus() error {
 		c.triggerDiscovery()
 		return fmt.Errorf("failed to update status: %v", err)
 	}
-	end := time.Now()
+	endTime := time.Now()
 
 	if len(resp.EvalIDs) != 0 {
 		c.logger.Debug("evaluations triggered by node update", "num_evals", len(resp.EvalIDs))
@@ -2156,7 +2156,7 @@ func (c *Client) updateNodeStatus() error {
 	last := c.lastHeartbeat()
 	oldTTL := c.heartbeatTTL
 	haveHeartbeated := c.haveHeartbeated
-	c.heartbeatStop.setLastOk(time.Now())
+	c.heartbeatStop.setLastOk(endTime)
 	c.heartbeatTTL = resp.HeartbeatTTL
 	c.haveHeartbeated = true
 	c.heartbeatLock.Unlock()
@@ -2168,7 +2168,7 @@ func (c *Client) updateNodeStatus() error {
 		// We have potentially missed our TTL log how delayed we were
 		if haveHeartbeated {
 			c.logger.Warn("missed heartbeat",
-				"req_latency", end.Sub(start), "heartbeat_ttl", oldTTL, "since_last_heartbeat", time.Since(last))
+				"req_latency", endTime.Sub(start), "heartbeat_ttl", oldTTL, "since_last_heartbeat", time.Since(last))
 		}
 	}