Use Run access for closed transient dynamic assemblies

Opt-in current-runtime port of AppDomain.CurrentDomain.DefineDynamicAssembly(name, RunAndSave) assigned to a method-local AssemblyBuilder whose only source read is a single resolved transient DefineDynamicModule(string) call. Replace the factory with AssemblyBuilder.DefineDynamicAssembly(name, Run), retaining local/module nodes and emitted IL. Require complete local references; skip persistence modules, save/identity/configuration/escape uses, deferred/async/iterator contexts, named/commented factory syntax and unsafe conditional snapshots. This deliberately drops unused save capability; persistence, reflection over assembly capabilities, Framework security policy and allocation/native failure details are not emulated. Standalone, not in version composites.