Add graph dump and load functionality

[purpleidea]

This change adds the ability to dump a resource graph from the engine to a YAML file and load it back. This is particularly useful for debugging and for creating standalone tests that operate on complex graph structures.

The implementation includes:

• A Dump(path string) method on the graph.Engine struct.
• DumpGraph(g *pgraph.Graph, path string) and LoadGraph(path string) functions in the engine/graph package.
• Intelligent parameter serialization that maps internal Go field names to their language-level equivalents (using lang struct tags) for a more "sensible" text format.
• Robust loading logic that reconstructs resources, restores parameters via the engine's type system (types.Into), and correctly handles nested/grouped resources.
• New tests in engine/graph/dump_test.go that verify dump/load integrity, grouping preservation, and provide a performance measurement of the autogrouping algorithm on loaded graphs.

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PR created automatically by Jules for task 13057943563418791222 started by @purpleidea

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