Prepare batched-copy tuning policy for lookahead

[bernhardmgruber]

Fixes part of: #10075

[coderabbitai]

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⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 4e8fed93-6748-4ddd-b770-fde51cf6e545

📥 Commits

Reviewing files that changed from the base of the PR and between bae29ea and 66d7ea5.

📒 Files selected for processing (7)

• cub/benchmarks/bench/copy/memcpy.cu
• cub/cub/device/dispatch/dispatch_batch_memcpy.cuh
• cub/cub/device/dispatch/tuning/tuning_batch_memcpy.cuh
• cub/test/catch2_test_device_copy_env.cu
• cub/test/catch2_test_device_copy_env_api.cu
• cub/test/catch2_test_device_memcpy_env.cu
• cub/test/catch2_test_device_memcpy_env_api.cu

🚧 Files skipped from review as they are similar to previous changes (7)

• cub/test/catch2_test_device_copy_env_api.cu
• cub/test/catch2_test_device_copy_env.cu
• cub/test/catch2_test_device_memcpy_env_api.cu
• cub/benchmarks/bench/copy/memcpy.cu
• cub/cub/device/dispatch/dispatch_batch_memcpy.cuh
• cub/test/catch2_test_device_memcpy_env.cu
• cub/cub/device/dispatch/tuning/tuning_batch_memcpy.cuh

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📝 Walkthrough

Summary by CodeRabbit

• New Features
  • Added explicit batched-copy algorithm selection for tuning policies.
  • Introduced a structured lookback configuration that organizes small- and large-buffer settings under a unified lookback policy.
• Refactor
  • Updated the batched-copy tuning policy representation to use { algorithm, lookback } instead of separate small/large fields.
• Bug Fixes
  • Improved consistency in batched-copy kernel launch configuration and sizing by deriving parameters directly from the selected lookback tuning.
• Tests
  • Updated batched-copy policy selector examples and policy expectation tests to match the new format.

Walkthrough

Changes

Batched memcpy policies now include an explicit BatchedCopyAlgorithm::lookback selector and nested tuning fields. Dispatch paths, benchmarks, and tests use the updated policy layout and formatting.

Batched memcpy policy refactor

Layer / File(s)	Summary
Algorithm-tagged policy contract cub/cub/device/dispatch/tuning/tuning_batch_memcpy.cuh	Adds BatchedCopyLookbackPolicy and BatchedCopyAlgorithm, changes BatchedCopyPolicy to {algorithm, lookback}, and updates selection, comparison, and formatting.
Lookback policy dispatch integration cub/cub/device/dispatch/dispatch_batch_memcpy.cuh	Kernel launch bounds, compile-time policies, tile sizing, occupancy sizing, and launch dimensions now use nested lookback tuning values.
Policy construction and validation updates cub/benchmarks/bench/copy/memcpy.cu, cub/test/catch2_test_device_copy_env.cu, cub/test/catch2_test_device_copy_env_api.cu, cub/test/catch2_test_device_memcpy_env.cu, cub/test/catch2_test_device_memcpy_env_api.cu	Benchmark and test policy builders explicitly initialize the lookback algorithm and nested tuning fields; property expectations cover the nested string representation.

Suggested reviewers: oleksandr-pavlyk, srinivasyadav18

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[coderabbitai]

Actionable comments posted: 2

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 7805cf30-f152-49db-87cf-def41ea226e8

📥 Commits

Reviewing files that changed from the base of the PR and between 56ff1a4 and bae29ea.

📒 Files selected for processing (7)

• cub/benchmarks/bench/copy/memcpy.cu
• cub/cub/device/dispatch/dispatch_batch_memcpy.cuh
• cub/cub/device/dispatch/tuning/tuning_batch_memcpy.cuh
• cub/test/catch2_test_device_copy_env.cu
• cub/test/catch2_test_device_copy_env_api.cu
• cub/test/catch2_test_device_memcpy_env.cu
• cub/test/catch2_test_device_memcpy_env_api.cu

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