fix(sema): reject void typed arguments to abi.encode

[aryanbaranwal001]

This PR fixes a compiler panic when a void returning expression is passed as an argument to abi.encode*.

• Fixes Compiler panic in codegen: Expression does not have a type when abi.encodePacked receives a void-returning call #1878

The root cause is that sema's abi.encode* argument resolution loop at sema/builtin.rs:1403 only guards against mapping and recursive types. It has no guard for Type::Void. So when a void returning expression like require(true) or a user defined void function g() is passed as an argument, sema accepts it without error and stores it in the AST as ast::Expression::Builtin { kind: Require, tys: [Type::Void], ... }.

codegen/expression.rs:1050, codegen's expression() matches ast::Builtin::AbiEncodePacked and calls abi_encode_packed() at codegen/expression.rs:1853.

abi_encode_packed then maps expression() over each arg. For Builtin::Require, this calls revert::require() at codegen/revert.rs:235, which emits the branch IR and returns Expression::Poison. That Poison is put into the packed args list.

abi_encode_packed passes the list to abi_encode() at codegen/expression.rs:1858.

abi_encode calls calculate_size_args() at codegen/encoding/mod.rs:48.

calculate_size_args calls get_expr_size() at codegen/encoding/mod.rs:176.

get_expr_size immediately calls expr.ty() on Expression::Poison, which hits Expression::Poison => unreachable!("Expression does not have a type") at codegen/mod.rs:1003 and panics.

Fix

Add a Type::Void guard in the arg resolution loop at sema/builtin.rs:1404, after the arg is resolved and before the is_mapping check:

if expr.tys().len() == 1 && expr.tys()[0] == Type::Void {
    diagnostics.push(Diagnostic::error(
        arg.loc(),
        "cannot pass a void expression as an abi.encode argument".to_string(),
    ));
    return Err(());
}

This makes sema reject void arguments before they reach codegen. The fix covers all affected variants, abi.encode, abi.encodePacked, abi.encodeWithSelector and abi.encodeWithSignature, since they all share the same loop at sema/builtin.rs:1403.

Previously panicking inputs:

• abi.encodePacked(require(true));
• abi.encode(require(true));
• abi.encodePacked(g()); where function g() public {}

Reproduces on polkadot, solana, and evm targets.