【Hackathon 9th No.59】Unit test for speculate_set_value_by_flags_and_idx

[cloudforge1]

Add unit tests for the speculative decoding value-setting op.

Source: look for speculate_set_value_by_flags_and_idx in custom_ops/gpu_ops/
Registration: custom_ops/gpu_ops/cpp_extensions.cc
Test file: tests/operators/test_speculate_set_value_by_flags_and_idx.py

Selectively sets values in a tensor based on flags and indices during speculative decoding. Test with different flag patterns and verify correct selective writes.

Branch: task/059-speculate-set-value-flags-test