Hydra: Mutable instantiate policy sets allow target blocklist bypass

Hydra is a framework for elegantly configuring complex applications. From 1.3.4 until 1.3.7 and 1.4.0.dev10, Hydra stores legacy instantiate target blocklists and related execution-policy collections in mutable module-level state. An attacker who controls multiple sibling target entries can resolve hydra._internal.target_policy.UNCONTROLLED_EXECUTION_TARGETS.discard through instantiate(), remove a denied target, and then invoke that target because sibling nodes are processed in insertion order against the same modified policy. The mutation persists in process-global state and can enable code execution with the application's privileges, while a narrow execution whitelist supplied by trusted Python code is not bypassed by the reported direct mutation path. This issue is fixed in versions 1.3.7 and 1.4.0.dev10.