Rust: main() body has no static-type scope, so string joins and int-to-long widening fail to compile there (E0308/E0277) #338

What's wrong

Every Standard generator except Rust opens a static-type scope around an EntryPoint body:

• Go: GoGenerator.cs:2136
• C: CGenerator.cs:1205
• C++: CppGenerator.cs:808
• Python: PythonGenerator.cs:855
• JavaScript: JavaScriptGenerator.cs:734

RustGenerator.GenerateEntryPoint (RustGenerator.cs L2142-L2181) never calls OpenStaticTypeScope(entryPoint); Rust only opens one for functions (L1101). RegisterStaticType does nothing when no scope is open, so no local inside fn main(), or inside the run helper generated for an exit-code entry point, has a known type.

Two Rust fixes depend on knowing those types: the format! string join (429d953, #240) and explicit as i64 widening (PR #329, #238). Neither applies inside an entry point.

Reproduction

var ep = new EntryPoint();
ep.Body.Add(new VariableDeclaration("name", "string", new LiteralExpression<string>("World")));
ep.Body.Add(new VariableDeclaration("bang", "string", new LiteralExpression<string>("!")));
ep.Body.Add(new VariableDeclaration("greeting", "string", new BinaryExpression(new VariableReference("name"), BinaryOperator.Add, new VariableReference("bang"))));
ep.Body.Add(new VariableDeclaration("small", "int", new LiteralExpression<int>(2)));
ep.Body.Add(new VariableDeclaration("big", "long", new LiteralExpression<long>(5000000000L)));
ep.Body.Add(new VariableDeclaration("sum", "long", new BinaryExpression(new VariableReference("big"), BinaryOperator.Add, new VariableReference("small"))));

The Rust output contains:

let mut greeting: String = (name + bang);   // E0308
let mut sum: i64 = (big + small);           // E0277 cannot add `i32` to `i64`

rustc --edition 2021 rejects it. The same statements inside a FunctionDeclaration produce format!("{}{}", name, bang) and (big + (small as i64)), which compile. Go produces int64(small) for the same entry point.

Suggested fix / acceptance criteria

• RustGenerator.GenerateEntryPoint opens OpenStaticTypeScope(entryPoint) around the body in both the plain main branch and the exit-code run branch, as GoGenerator does.
• When AcceptsArguments is set, args is bound as Vec<String>.
• RustGeneratedSourceCompilesTests compiles an entry point that joins two String locals and adds an int local to a long local.