fix(pre-commit): normalize SPDX handling

[bdice]

Description

Contributes to rapidsai/build-planning#303.

Standardizes clang-format's SPDX protection and ensures the repository uses rapidsai/pre-commit-hooks v1.6.0. It also restores malformed SPDX headers where present.

Validated with pre-commit run --all-files.

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[jameslamb]

One test failure:

[==========] 9 tests from 3 test suites ran. (1069 ms total)
[  PASSED  ] 8 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] silhouetteScore.BatchedStreamPoolOrdering

 1 FAILED TEST
CMake Error at run_gpu_test.cmake:26 (execute_process):
  execute_process failed command indexes:

    1: "Child return code: 1"

Errors while running CTest

97% tests passed, 1 tests failed out of 34

Total Test time (real) = 6280.02 sec

The following tests FAILED:
	 34 - STATS_TEST (Failed)

(build link)

I've triggered a re-run, hopefully we'll see it pass.

[jameslamb]

/merge