Durable Agent lacks default resiliency policy for activities

[bibryam]

Description:
Durable Agent currently does not apply any resiliency policy to activities by default. As a result, a single failure in any activity causes the entire agent workflow to fail.

This behavior reduces robustness for long-running workflows where transient errors are expected.

Expected Behavior:

Every activity should, by default, have a resiliency policy applied with infinite retries.
Durable Agent should expose configuration to adjust this default, allowing users to:

• Disable retries (0).
• Set a fixed number of retries.