Add batch_id to explode parameters

[const-cloudinary]

Problem

uploader.explode builds its params inline and does not serialize batch_id, so a client-supplied value never reaches the wire:

uploader.explode("doc", page="all", format="jpg", batch_id="mybatch")
# -> {"status": "processing", "batch_id": "95e726aa…47245a"}   # server-minted, not ours

This matters because batch_id is what makes the completion notification pollable. explode is unconditionally async — it always enqueues a job and returns {"status": "processing", …} — so polling is the only way to observe completion.

Why the response batch_id isn't a substitute

The response and the notification payload both echo a batch_id even when the client sends none, but that value is not a poll partition key. The poll destination reads the key from ThreadContext, which is populated only from a client-supplied value; the server-minted fallback feeds the response body and payload via a different path. With no client value the notification is enqueued unpartitioned and cannot be polled.

Verification

Live against a real product environment, with a poll://* / explode trigger in place.

Before — three attempts, including one with notification_url='poll://*' passed explicitly, all timed out with an empty buffer despite the job succeeding (3 derived pages produced):

$ cld uploader explode explode_probe page=all format=jpg
{"status": "processing", "batch_id": "95e726aa…47245a"}
$ cld notifications poll --batch-id 95e726aa…47245a --timeout 40
error: Timed out after 40s with 0 event(s) received.

After:

$ cld uploader explode explode_probe page=all format=jpg batch_id=fixprobe777
{"status": "processing", "batch_id": "fixprobe777"}     # our value, echoed back
$ cld notifications poll --batch-id fixprobe777 --timeout 60
explode
Received 1 event(s).

upload --wait on the same cloud succeeded throughout, confirming the poll transport itself was healthy and the gap was specific to explode.

Tests

Adds test_explode_parameters — there was no explode coverage previously. It asserts public_id, format, notification_url and batch_id all reach the request params, and fails with KeyError: 'batch_id' without this change.

Only batch_id is added: the server ignores async on this endpoint since explode is always asynchronous.

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