Sandbox escape via stale member accessor cache

Authorization bypass in Scriban before 7.0.0 allows attackers to read or write filtered object members via reused TemplateContext instances. TemplateContext.GetMemberAccessor caches TypedObjectAccessor instances only by Type even though GetMemberAccessorImpl builds each accessor with the current MemberFilter and MemberRenamer, so later renders reuse a stale exposed-member set. Exposure requires an application to reuse a TemplateContext and tighten MemberFilter between renders, which can leak hidden properties across requests or tenants and allow writes when a filtered member has a setter.