extract shared cairo-starknet-syscalls crate

Both cairo-native and sierra-emu now re-export the StarknetSyscallHandler
trait and supporting types (U256, Block/Tx/Execution Info v{1,2,3},
ResourceBounds, Secp256{k1,r1}Point) from the new
`cairo-starknet-syscalls` crate. The crate is workspace-local at the
top level (sibling to `test_utils/`).

The two crates' types are now nominally identical, so a single handler
impl can drive both runtimes without an adapter / bridge.

Notes:
- `cairo-starknet-syscalls` rather than `cairo-native-syscalls`: the
  crate's content doesn't depend on cairo-native semantically; the
  cairo-native prefix would imply ownership it doesn't have.
- StubSyscallHandler's `unimplemented!()` stubs now carry a one-line
  rationale each (deploy needs constructor execution, call_contract
  needs address-to-class resolution, send_message_to_l1 needs an L1
  queue, etc.), plus a scope doc-comment on the type itself.
- sierra-emu's previous inherent into_value/from_value methods (which
  depend on sierra-emu's `Value` enum and can't follow the moved types)
  become free functions in the new sub-module
  `sierra_emu::starknet::value_conv`, each with a doc comment.
- `cheatcode` trait method's default impl returns an error felt instead
  of panicking with unimplemented!(). On the sierra-emu path, a contract
  invoking the cheatcode libfunc against a handler that didn't override
  it would otherwise unwind through the VM and abort the host;
  production handlers (e.g. blockifier's NativeSyscallHandler) don't
  implement cheatcode, so the default is what runs.
- The per-type files under debug_utils/sierra-emu/src/starknet/* are
  deleted now that the struct definitions live in the shared crate.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: avi-starkware

Cargo.lock

@@ -3,6 +3,7 @@ exclude = [
     "debug_utils/casm-data-flow",
 ]
 members = [
+    "cairo-starknet-syscalls",
     "debug_utils",
     "debug_utils/sierra-emu",
     "debug_utils/cairo-native-stress",
@@ -53,6 +54,7 @@ cairo-lang-test-runner = "~2.19.0-rc.0"
 cairo-lang-utils = "~2.19.0-rc.0"
 cairo-native-bin-utils.path = "binaries/cairo-native-bin-utils"
 cairo-native = { path = ".", version = "0.9.0-rc.7" }
+cairo-starknet-syscalls = { path = "cairo-starknet-syscalls", version = "0.9.0-rc.7" }
 clap = "4.5.23"
 colored = "2.1.0"
 criterion = "0.5.1"
@@ -135,6 +137,7 @@ testing = ["dep:cairo-lang-compiler", "dep:cairo-lang-filesystem"]
 [dependencies]
 aquamarine.workspace = true
 bumpalo.workspace = true
+cairo-starknet-syscalls.workspace = true
 cairo-lang-compiler = { workspace = true, optional = true }
 cairo-lang-filesystem = { workspace = true, optional = true }
 cairo-lang-lowering.workspace = true

Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "cairo-starknet-syscalls"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+description = "Shared StarknetSyscallHandler trait and supporting types for cairo-native and sierra-emu"
+
+[dependencies]
+serde = { workspace = true, features = ["derive"] }
+starknet-types-core = { workspace = true, features = ["std", "serde", "num-traits"] }