extract shared cairo-native-syscalls crate

[avi-starkware]

Summary

Extracts the StarknetSyscallHandler trait and its supporting types into a new workspace-local crate, cairo-native-syscalls. Both cairo-native and sierra-emu re-export from it, so the two crates' types are now nominally identical — a single handler impl can drive both runtimes without an adapter.

Replaces the bridge approach from #1597 / #1607: with this PR landed, the bridge file isn't necessary, and #1608's Emu arm can call the cairo-native handler directly. Those follow-ups land in subsequent PRs in this stack.

Layout

cairo-native-syscalls/
  Cargo.toml      # deps: serde, starknet-types-core
  src/lib.rs      # types + trait

Sibling to test_utils/ at workspace root — fits the repo's existing convention for shared, non-binary, non-debug-tool crates.

What moved

From cairo-native/src/starknet.rs and sierra-emu/src/starknet/* into the new crate:

• Types: U256, BlockInfo, TxInfo, TxV2Info, TxV3Info, ResourceBounds, ExecutionInfo, ExecutionInfoV2, ExecutionInfoV3, Secp256k1Point, Secp256r1Point.
• Trait: StarknetSyscallHandler, including its existing default cheatcode impl.
• Constructors: Secp256k1Point::new / Secp256r1Point::new (pure-data).
• Alias: SyscallResult<T>.

Repr / serde / derive layouts preserved exactly (#[repr(C, align(16))] on U256, Secp256{k1,r1}Point).

What stayed put

• cairo-native: ArrayAbi, Felt252Abi, DummySyscallHandler, the runtime/codegen vtables (handler::StarknetSyscallHandlerCallbacks, cairo_native__vtable_cheatcode, etc.) — all cairo-native-specific.
• sierra-emu: StubSyscallHandler, StubEvent, ContractLogs, and the VM eval logic.

Value-conversion methods

Sierra-emu previously had impl <Type> { fn into_value(self) -> Value, fn from_value(v: Value) -> Self } on each type. Inherent impls can't follow the type into a foreign crate, so these become free functions in a new sierra_emu::starknet::value_conv module:

Before	After
U256::from_value(v)	u256_from_value(v)
u.into_value()	u256_into_value(u)
Secp256k1Point::from_value(v)	secp256k1_point_from_value(v)
info.into_value(felt_ty)	execution_info_into_value(info, felt_ty)
...	(same pattern for each type)

Call sites in sierra-emu/src/vm/starknet.rs and cairo-native/src/metadata/trace_dump.rs updated.

Backwards compatibility

• cairo-native users: backwards-compatible. cairo_native::starknet::U256, …::StarknetSyscallHandler, etc. still resolve via pub use. Existing impls and callers compile unchanged. No semver-breaking change.
• sierra-emu users: breaking — the inherent into_value / from_value methods are gone. Sierra-emu is debug-only and not an externally published API surface; callers in this repo are all updated.
• The 11 per-type files under debug_utils/sierra-emu/src/starknet/* are deleted now that the struct defs live in the shared crate.

Stack

1. align sierra-emu StarknetSyscallHandler trait/types with cairo-native #1610 — align trait/type surfaces ← prerequisite
2. this PR — extract the shared crate
3. (next) ContractExecutor dispatch enum without the bridge (replaces add ContractExecutor dispatch enum (Aot + Emu) #1598 / add ContractExecutor dispatch enum (Aot + Emu) #1608)
4. (next) run_with_libfunc_profile + AotWithProgram (rebase of add run_with_libfunc_profile + AotWithProgram variant for ContractExecutor #1599 / add run_with_libfunc_profile + AotWithProgram variant for ContractExecutor #1609)

Test plan

• cargo check --workspace --all-features clean
• cargo check -p sierra-emu --all-targets clean
• CI green

[github-actions]

✅ Code is now correctly formatted.