Allow fully configurable defaults for tool spawn settings

[virajmehta]

Fixes a bug: defaults on max_attempts were not being propagated to child tool spawns.
As part of the fix, I extended the API to allow callers to configure defaults for more than just max_attempts:

  let client = Durable::builder()
        .pool(pool.clone())
        .queue_name("fanout_by_name")
        .default_max_attempts(7)
        .default_retry_strategy(RetryStrategy::Exponential {
            base_delay: Duration::from_secs(10),
            factor: 3.0,
            max_backoff: Duration::from_secs(600),
        })
        .default_cancellation(CancellationPolicy {
            max_pending_time: Some(Duration::from_secs(3600)),
            max_running_time: None,
        })
        .build()
        .await
        .expect("Failed to create client");

These are now applied to all spawns and fully configurable.

[virajmehta]

I am investigating this failure

[virajmehta]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 👍

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