Type Checker: skip zero-param free functions in attachedFunctions resolution

[genisis0x]

Description

Fixes #16610.

solc --bin panics with an internal compiler error when a using { zero } for T directive binds a zero-parameter free function and the call site (x.zero()) appears in the contract body before the directive:

function zero() pure returns (uint) { return 0; }

contract C {
    function f(uint z) external pure returns (uint) {
        return z.zero();
    }
    using {zero} for uint;
}

Internal compiler error:
libsolidity/ast/Types.cpp(3753): Throw in function ... withBoundFirstArgument()
Solidity assertion failed

Type::attachedFunctions() is called from member resolution while typechecking z.zero(). For library-bound entries it already filters out functions with no parameters at Types.cpp:460, but the non-library branch (free functions bound via using { zero } for T) calls addFunction() unconditionally, which asserts in FunctionType::withBoundFirstArgument(). The fatal 4731 ("does not have any parameters") in TypeChecker::endVisit(UsingForDirective) only fires later, when the directive itself is visited.

This change mirrors the existing library-binding filter for free-function bindings: empty-parameter entries are skipped during attached-function resolution. The TypeChecker still emits the 4731 error from the directive, and the call site separately emits a 9582 "member not found" error, matching the diagnostics surface that users would see for any other unattached function.

Tests

• New test/libsolidity/syntaxTests/using/using_free_no_parameters_call_site_before_directive.sol reproduces the issue MRE and asserts both expected TypeError 9582 and TypeError 4731 instead of the prior ICE.
• Existing using_free_no_parameters_err.sol (directive without call site) is unaffected.

Checklist

• I have read the contributing guidelines and the review checklist
• I have personally reviewed, understood, and tested every change in this PR

AI Disclosure

• No AI tools were used
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