Retry forever by default and not 3 times

[alob-mtc]

Description

Make the retry option optional and fix the retry forever behavior.

Current Behavior

• max_retries is a u32 field
• max_retries == 0 means retry forever (logically incorrect)
• Default is 3 retries

Desired Behavior

• Make max_retries an Option<u32> field
• If max_retries is None (not set), the activity should retry forever
• If max_retries is Some(0), the activity should not retry (0 means no retry)
• If max_retries is Some(n) where n > 0, the activity should retry up to n times

Rationale

The current logic where 0 == retry forever is counterintuitive. The new approach is more logical:

• None = retry forever (unlimited)
• Some(0) = no retry
• Some(n) = retry up to n times

Implementation Notes

• Update ActivityOption.max_retries from u32 to Option<u32>
• Update Activity.max_retries from u32 to Option<u32>
• Update the retry logic in src/queue/queue.rs (around line 1187) to check for None (retry forever) instead of 0
• Update default behavior to use None for retry forever instead of 3