fuzzers: AI-assisted cleanups

[smalis-msft]

General cleanups to all of our fuzzers that should make them more efficient and have slightly better coverage, as well as fix some missing init_tracing_if_repro calls.

[github-actions]

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[Copilot]

Pull request overview

This PR performs targeted cleanups across multiple fuzz targets in the OpenVMM workspace to improve fuzzing efficiency/corpus quality and to make repro runs more diagnosable by consistently initializing tracing.

Changes:

• Improve input utilization and behavior modeling in several fuzzers (e.g., more realistic/varied request bytes and richer action selection).
• Add/standardize xtask_fuzz::init_tracing_if_repro() calls in fuzz targets that were missing them.
• Switch some fuzzers to return libfuzzer_sys::Corpus and reject unproductive inputs, and simplify fuzz-crate deps accordingly.

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
vm/devices/storage/storvsp/fuzz/fuzz_storvsp.rs	Makes REPORT_LUNS CDB contents less trivial by consuming more fuzz input.
vm/devices/storage/scsi_buffers/fuzz/fuzz_scsi_buffers.rs	Adds init_tracing_if_repro() in the fuzz entrypoint.
vm/devices/storage/disk_nvme/nvme_driver/fuzz/fuzz_nvme_driver.rs	Reworks to pass Unstructured through APIs; simplifies GUID generation from fuzz bytes.
vm/devices/storage/disk_nvme/nvme_driver/fuzz/fuzz_main.rs	Removes global input state; uses Unstructured directly and rejects malformed inputs via Corpus.
vm/devices/storage/disk_nvme/nvme_driver/fuzz/Cargo.toml	Drops parking_lot and removes unused-deps ignore now that libfuzzer-sys is referenced directly.
vm/devices/firmware/firmware_uefi/fuzz/fuzz_diagnostics.rs	Rejects empty-memory cases via Corpus and returns arbitrary::Result<()> from do_fuzz.
vm/devices/firmware/firmware_uefi/fuzz/Cargo.toml	Removes unused-deps ignore now that libfuzzer-sys is referenced directly.
vm/devices/chipset/fuzz/fuzz_cmos_rtc.rs	Introduces explicit fuzz actions (chipset event vs time manipulation) to exercise more time-related behavior.
vm/devices/chipset/fuzz/fuzz_battery.rs	Introduces explicit fuzz actions to interleave chipset events with battery updates.
support/ucs2/fuzz/fuzz_ucs2.rs	Adds init_tracing_if_repro() in the fuzz entrypoint.
support/sparse_mmap/fuzz/fuzz_sparse_mmap.rs	Simplifies expected-error handling and adds missing init_tracing_if_repro().
Cargo.lock	Removes parking_lot from the nvme_driver fuzz crate dependency set.