Fix TypeError in exponential_delay function when handling connection timeouts

Problem:
- Agent v1.8.3-1~noble crashes on Ubuntu 24.04 with TypeError when receiver.amplify.nginx.com times out
- Error occurs in backoff.py: "TypeError: 'float' object cannot be interpreted as an integer"
- The issue prevents proper exponential backoff during network connectivity problems
- Agent completely stops instead of retrying with the backoff delay

Solution:
- Add explicit integer type conversion to period_size before passing to randint()
- Convert: return randint(0, period_size - 1)
- To: return randint(0, int(period_size) - 1)

This fix allows the agent to properly handle connection timeouts without crashing.
The issue appears to be specific to Python 3.12 used in Ubuntu 24.04 Noble, as
the agent works correctly on Ubuntu 22.04 Jammy with Python 3.10.

Fixes #124

amplify/agent/common/util/backoff.py

@@ -32,4 +32,4 @@ def exponential_delay(n):
         (EXPONENTIAL_COEFFICIENT ** n)
     period_size = min(exponential_limit, MAXIMUM_TIMEOUT)
 
-    return randint(0, period_size - 1)
+    return randint(0, int(period_size) - 1)