[NEW MODEL] Add decision tree example

[haoruilee]

Add Decision Tree example and Iris inference setup to address "pending" ML features in ora-io/opml

• Implements a Decision Tree model training example on the Iris dataset.
• Adds a GGML-based inference flow in Go for MIPS environments.
• Provides a quick start reference to fulfill the "pending" ML feature (Decision Tree) from ora-io/opml’s README.