Add move closures, allocators, join results, and protocol endpoints

[Cod-e-Codes]

Summary

• The checker copies aggregates of Copy fields, treats a literal index as its own borrow path, and marks a consuming call inside an operator or index so Box::unwrap in an expression is freed once.
• ? accepts an owned enum with one success variant. for accepts Iter<T>. A fn literal that names an outer owned binding is a move closure. spawn is JoinHandle<T>, and scope joins handles still owned in the block.
• Vec, String, and Box store an Allocator. endpoint<Name>() is a unique protocol endpoint on two crossed channels. This is 0.4.0: regenerate C for Vec, String, and Box, and relink.

Test plan

• cargo fmt --check
• cargo test
• cargo clippy -- -D warnings
• tests/test_runner.sh on Linux, macOS, and Windows
• Sanitizer and warning-clean generated C in CI