fix: notify task scheduling

[LexLuthr]

This PR fixes a couple of problem.

1. Notify task is a very important step for piece processing but it was an IAMBored scheduled. PDP nodes are a lot more noisy due to PPInit and PPNext failures and this caused harmony scheduler to no prioritize Notify for scheduling. I have moved scheduling to a goroutine.
2. Order of Notify is before Proving task. This means when people run this PR and they have huge backlog of Notify tasks, they will fail to prove on time. This PR fixes the problem.

Outside of PR's scope:

1. Rethink Curio's IAmBored at scale. Especially on PDP nodes.
2. Get rid of DataSet Init from Curio and keep this in FWSS and PDPVerifier layer.

[Copilot]

Pull request overview

This PR fixes notify task scheduling issues in the PDP (Proof of Data Possession) system by moving task scheduling from an IAmBored callback to a dedicated goroutine and adjusting task execution order to prioritize proving over notification.

Key changes:

• Replaces IAmBored-based scheduling with a continuous polling goroutine for notify tasks
• Reorders task registration to execute proving tasks before notify tasks, preventing notification backlogs from blocking proof submissions
• Adds exponential retry backoff to init and next proving period tasks

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
tasks/pdp/notify_task.go	Refactored from IAmBored scheduling to goroutine-based polling; added Promise pattern for task function management; removed LIMIT 1 from query to process all pending uploads
cmd/curio/tasks/tasks.go	Reordered task registration to place pdpProveTask before pdpNotifTask
tasks/pdp/task_init_pp.go	Added exponential retry wait with 5s initial delay and factor of 2
tasks/pdp/task_next_pp.go	Added exponential retry wait with 5s initial delay and factor of 2

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[rvagg]

Can we add AND pu.notify_url IS NOT "" too?

We don't use notify in Synapse, there may be more advanced FWSS users who are using it, perhaps with their own interaction model, but I'm not aware of them. Maybe this task running every time is more of a problem since it doesn't have a URL to do anything with.