fix(spur-tests): remove unused imports and variables

[shiv-tyagi]

Drop unused HashMap, Arc, JobId, and partition imports from the test harness and scheduler tests. Mark job binding as immutable in GPU test.

[Copilot]

Pull request overview

Cleans up the spur-tests crate by removing unused imports and making a GPU test job binding immutable, reducing warnings and keeping test code minimal.

Changes:

• Removed unused HashMap, Arc, and JobId imports from the test harness.
• Removed an unused partition::* import from scheduler tests.
• Changed a GPU test’s job binding from mut to immutable.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/spur-tests/src/t39_gpu.rs	Makes the test job binding immutable where it is not mutated.
crates/spur-tests/src/t07_sched.rs	Drops an unused partition module import from scheduler tests.
crates/spur-tests/src/harness.rs	Removes unused std/core imports from the test harness module.

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[shiv-tyagi]

Reviewed myself and with copilot. Looking good. Merging.