Merge dev-v2.19.3 into main

[eytan-starkware]

Brings the v2.19.3 release back into main: the casm-contract-class refactor, the sierra 1.9.2 bump, and the v2.19.3 version bump. Conflict-free merge; starknet/starknet-classes suites pass.

Follow-up context: main is heading to v2.20.0-rc.1 via dev-v2.20.0, which will pick these up on the next merge of main.

🤖 Generated with Claude Code

[cursor]

PR Summary

Medium Risk
Sierra 1.9.2 and stricter entry-point error-type checks affect compiled contract metadata and which signatures validate; mostly release bookkeeping otherwise.

Overview
Merges the v2.19.3 release line into main: workspace, corelib, Cargo.lock, and scripts/bump_version.sh all move from 2.19.2 to 2.19.3.

Starknet contract compilation gets two substantive updates. current_sierra_version_id() is bumped to 1.9.2 (patch 1.9.1 → 1.9.2). Entry-point return validation in casm_contract_class now requires the panic half of a (panic, data) error struct to be an empty struct, matching the ABI layout where the error variant is only Array<felt252>; a new is_empty_struct helper enforces that.

Starknet test fixtures (contract_class.json / compiled_contract_class.json) are refreshed for the new compiler and Sierra versions (including Sierra program header fields and compiler_version strings).

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