fix(AUD-023): plugins empaquetados con entornos virtuales aislados

[Axlfc]

Implemented packaged plugin format support with virtual environment isolation for extension plugins in cognito-backend. Defined manifest format (plugin.json/manifest.json), PluginEnvironment for venv creation and dependency installation via pip subprocess, IsolatedExtensionAPI for sys.modules/sys.path isolation, and updated ExtensionLoader discovery and loading. Updated AUDIT_MASTER.md for AUD-023.

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PR created automatically by Jules for task 6795667326467112622 started by @Axlfc

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