Enable prefetching of SW kernel instructions after the first SW task

[Kepontry]

Summary

This PR enhances the AddSwKernelInstructionPrefetchPass to enable prefetching of SHAVE kernel instructions after the first SHAVE task, if the initial slack is insufficient.

Currently, instruction prefetching is skipped if the slack before the first SHAVE task is insufficient. This limitation is suboptimal when initial insertion slots (tiles) are limited or L2 cache capacity is constrained.

Based on the observation that SHAVE utilization is often low, we propose this change to prefetch opportunistically later in the schedule. This approach has demonstrated a ~3% performance gain on models such as Qwen2-1.5b and Qwen3-0.6b.

Target Platform For Release Notes

• NPU37XX
• NPU40XX
• NONE (Not included in release notes)

Classification of this Pull Request

• Maintenance
• BUG
• Feature

Implementation Details

• The new logic searches for insertion gaps that begin at a "non-saturated" point (where num_shave_tasks < available_shave_count).
• The gap ends at either a "saturated" point or the kernel designated for prefetching.
• The prefetch operation is inserted at the tile3 task of the identified insertion point.
• The minimal insertion slack required is set to 50K cycles.

Additional Fixes & Enhancements

• Corrected an issue in insertDummyKernelOpBeforeFirstKernelTask where the clusterIdx was not being used during tile assignment.
• Expanded Prefetching: Enriched the "kernel kind" logic to allow more types of kernels to be prefetched.

We also noted that the previous 250K-cycle threshold is overly conservative for our platform (Ultra 258V). Our analysis shows that prefetching provides benefits even with a slack as low as 170K cycles.

[DariaMityagina]

@Kepontry hello! Thanks for your PR!

Could you please ensure your changes include test coverage by adding tests to https://github.com/openvinotoolkit/npu_compiler/blob/develop/tests/lit/NPU/dialect/VPUIP/passes/add_sw_kernel_instruction_prefetch_40XX.mlir and maybe some functional tests?

[DariaMityagina]

@Kepontry hello! Thanks for your PR!

Could you please ensure your changes include test coverage by adding tests to https://github.com/openvinotoolkit/npu_compiler/blob/develop/tests/lit/NPU/dialect/VPUIP/passes/add_sw_kernel_instruction_prefetch_40XX.mlir and maybe some functional tests?

@Kepontry could you please look into this comment? Thank you!

[Kepontry]

Apologies for the delay; I missed the email notification for this thread. I am currently working on adding the test. Could you provide some guidance or documentation on how to use the lit test framework within the NPU compiler?

[Kepontry]

Functional test added.