[TIRx][Schedule] Support rfactor for arg reducers selecting last index

[ZephyrLi-pro]

This PR extends rfactor reducer pattern matching to support TOPI argmax/argmin with select_last_index=True.

For select_last_index=True, ties should be resolved by choosing the larger index. The added reducer patterns preserve the existing value comparison semantics, then use lhs_idx > rhs_idx as the tie-break condition.

Tests are added for applying rfactor to topi.argmax and topi.argmin with select_last_index=True.

[gemini-code-assist]

Code Review

This pull request introduces support for argmax and argmin reducers with select_last_index=True (preferring the last occurrence) in the TIR schedule reduction primitive. It adds the corresponding reducer implementations in reduction.cc and includes comprehensive unit tests in test_tir_schedule_rfactor.py to verify the correctness of rfactor scheduling on these new reducers. There are no review comments, so we have no additional feedback to provide.

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[yongwww]

@tvm-bot rerun