apollo_staking: implement get_previous_epoch_data in mock staking contract

[dafnamatsry]

Note

Medium Risk
Changes the mock contract ABI and storage layout by adding a new optional previous-epoch path, and regenerates the compiled CASM artifact; this can break tests/fixtures that assume the prior interface or bytecode offsets.

Overview
Extends the Cairo1 mock_staking test contract to support a previous epoch alongside the current epoch.

Adds set_previous_epoch plus a new view get_previous_epoch_data that returns Option<(Epoch, BlockNumber, u32)>, backed by new storage fields (has_previous_epoch, previous_epoch). Updates the compiled mock_staking.casm.json accordingly (new bytecode/entry points/segment lengths) to match the ABI change.

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[reviewable-StarkWare]

This change is 

[dafnamatsry]

• apollo_staking: implement get_previous_epoch in CairoStakingContract #12902
• apollo_staking: implement get_previous_epoch_data in mock staking contract #12901 👈 (View in Graphite)
• main-v0.14.2

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