fix: use atomic counter for tempdir uniqueness in bench_tail tests

[rominf]

Summary

• Replaces the SystemTime::now().as_nanos() suffix in tempdir() with an AtomicU64 counter
• Windows SystemTime has ~15ms resolution; parallel tests running within the same timer tick could collide on the same directory path, causing tests to read/write each other's results.csv and produce wrong deserialization results
• Observed failure: missing_30col_fields_default_safely got rows[0].run == 1 (from another test's ROW2) instead of 7

Root cause

bench_tail::tests::tempdir() built its path as rocm-dash-test-{pid}-{nanos}. Under full parallel test load on Windows CI, the three tests in the module ran within the same 15ms clock tick → same suffix → same directory → same results.csv → file contents from one test leaked into another.

An atomic counter increments on every call so each invocation gets a distinct suffix regardless of clock resolution.

Test plan

• cargo test -p rocm-dash-collectors passes (54/54)
• Windows CI green

Fixes flaky failure observed in https://github.com/ROCm/rocm-cli/actions/runs/27690632058/job/81900409577

[Copilot]

Pull request overview

This PR fixes a Windows-specific test flake in rocm-dash-collectors by ensuring each test invocation uses a uniquely named temporary directory even when multiple tests run within the same coarse SystemTime tick.

Changes:

• Replaced the SystemTime::now().as_nanos()-based temp directory suffix with a process-local AtomicU64 counter.
• Ensured parallel unit tests in bench_tail cannot collide on the same temp directory / results.csv path on Windows.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[rominf]

Closing as already-fixed. When rebasing onto current main, the only remaining diff is the tempdir prefix string — the atomic-counter fix that is the substance of this PR already landed on main via #15 (Enable strictest practical linting across the workspace), which uses the more descriptive prefix rocm-dash-bench-tail-{pid}-{n}. No code change is needed.