Read ReceiptAnchor max batch size from chain instead of hard-coding 1000

[VedantMadane]

Follow-up to accensa/accensa-contracts#161.

ReceiptAnchor now exposes get_max_batch_size(). The indexer that builds Merkle batches should call this getter (or cache it per deployment) rather than assuming 1000, so a future constant tune does not silently disagree with the contract.

Related: accensa/accensa-contracts#161

[pyper01]

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i will like to work on this

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