Implement Template based inference

Template based inference w/ composer experience and formalised template format. See [A2UI Service Profiles](https://docs.google.com/document/d/1ndMBjG6TSHqYuKelV44aXAfKYgbwpeSJ0mjsuEUau08/edit?resourcekey=0-wZ1i9OznitV9hklVWNra3g&tab=t.0#heading=h.etlgqpsrulcl) (internal Google document).

The issue references an internal Google document for details, which is not accessible. Without the linked design doc, the scope, template format, and composer experience are undefined. A newcomer would need to first understand the existing inference system and then design a new template-based approach, which requires significant domain knowledge and design work.

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