Resl2001 Unsafe Oneof.Ast Access Warning Code Fix

title: RESL2001 — Unsafe OneOf.AsT* Access [Warning + Code Fix]

---

var oneOf = GetResult();        // OneOf<User, NotFound, ValidationError>
var user = oneOf.AsT1;          // ⚠️ RESL2001: Access to '.AsT1' without checking '.IsT1'
                                // 💡 Fix: Replace with oneOf.Match(...)

// ✅ Safe alternatives:
if (oneOf.IsT1)
    var user = oneOf.AsT1;      // No warning — guarded

var user = oneOf.Match(         // No warning — exhaustive pattern match
    user => user,
    notFound => throw new NotFoundException(),
    error => throw new ValidationException());