Scaffold Cargo workspace with four crates

[Claude]

Establishes the foundational Cargo workspace structure for the Stator JavaScript engine with four member crates, build tooling, and repository configuration.

Workspace Structure

• Root Cargo.toml — Workspace with resolver = "2", defines four member crates
• rust-toolchain.toml — Pins to stable channel for edition 2024 support (rustc ≥ 1.85)
• .gitignore — Rust build artifacts, IDE files, test mutation data
• Root README.md — Project description

Member Crates

• crates/stator_core — Engine library (rlib)

  • GC infrastructure (heap, tracing, handles)
  • JavaScript value representation (tagged pointers, heap objects)
  • 14 unit tests covering allocation, collection, and value encoding

• crates/stator_ffi — C-ABI FFI surface (cdylib, staticlib)

  • Exports stator_isolate_create, stator_isolate_destroy, stator_isolate_gc
  • Opaque handle types for embedders (e.g., Chromium)
  • Depends on stator_core

• crates/stator_test262 — Test262 conformance harness (bin)

  • Placeholder for ECMAScript Test262 test suite integration
  • Depends on stator_core

• crates/st8 — CLI JavaScript shell (bin)

  • Interactive REPL analogous to V8's d8
  • Depends on stator_core

All crates use edition 2024 and compile with zero warnings. cargo build --workspace and cargo test --workspace succeed.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[P0] Scaffold Cargo workspace with four crates</issue_title>
<issue_description>Create the root Cargo.toml workspace with four member crates:

• crates/stator_core — engine lib (rlib)
• crates/stator_ffi — C-ABI FFI surface (cdylib, staticlib)
• crates/stator_test262 — Test262 conformance harness (bin)
• crates/st8 — CLI JavaScript shell (bin)

Include rust-toolchain.toml, .gitignore, and root README.md.

Acceptance criteria:

• cargo build --workspace succeeds
• cargo test --workspace succeeds
• All four crates compile with no warnings</issue_description>

Comments on the Issue (you are @claude[agent] in this section)

• Fixes [P0] Scaffold Cargo workspace with four crates #3