Fix the bug in pruning tree predictions.

[zhi-bao]

What does this PR do?

Fix the bug in PR #11.

• Bug: The last classifier in the rightmost node of tree models was not included in the subtree_weights.
  The original implementation

subtree_weights_end = self.node_ptr[self.root.children[i+1].index] if i+1 < len(self.root.children) else -1 slice = np.s_[:, subtree_weights_start:subtree_weights_end]

causes incorrect slicing for the last subtree, leading to last classifiers in rightmost node(i.e., the last classifier in the last subtree_weights ) being excluded.

• Solution: Useself.node_ptr[-1] to correctly include the last classifier.

Test CLI & API (bash tests/autotest.sh)

Test APIs used by main.py.

• Test Pass
  • (Copy and paste the last outputted line here.)
• Not Applicable (i.e., the PR does not include API changes.)

Check API Document

If any new APIs are added, please check if the description of the APIs is added to API document.

• API document is updated (linear, nn)
• Not Applicable (i.e., the PR does not include API changes.)

Test quickstart & API (bash tests/docs/test_changed_document.sh)

If any APIs in quickstarts or tutorials are modified, please run this test to check if the current examples can run correctly after the modified APIs are released.

[Eleven1Liu]

I will release this PR with PR 20, so no need to change this line.

[Eleven1Liu]

LGTM