Add tests around the Omnibus cache and make duration management safer

[alopezz]

What does this PR do?

• Adds test for most common scenarios around the Omnibus cache management.
• Small refactor around how durations are collected to reduce the likelihood of causing job failures unnecessarily.

Motivation

Two recent failures:

• A flaky one around cache corruption.
• Breaking main for all cache hits due to flawed logic around duration collection.

Additional Notes

Possible Drawbacks / Trade-offs

Describe how to test/QA your changes

[agent-platform-auto-pr]

[Fast Unit Tests Report]

On pipeline 33940124 (CI Visibility). The following jobs did not run any unit tests:

Jobs:

• tests_deb-arm64-py3
• tests_deb-x64-py3
• tests_flavor_dogstatsd_deb-x64
• tests_flavor_heroku_deb-x64
• tests_flavor_iot_deb-x64
• tests_rpm-arm64-py3
• tests_rpm-x64-py3
• tests_windows-x64

If you modified Go files and expected unit tests to run in these jobs, please double check the job logs. If you think tests should have been executed reach out to #agent-developer-experience

[pr-commenter]

Regression Detector

Regression Detector Results

Run ID: 578c4222-aeeb-43ff-9b58-85fe7d3c059e
Baseline: 1f10c8a
Comparison: 41cc394

Performance changes are noted in the perf column of each table:

• ✅ = significantly better comparison variant performance
• ❌ = significantly worse comparison variant performance
• ➖ = no significant change in performance

No significant changes in experiment optimization goals

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

There were no significant changes in experiment optimization goals at this confidence level and effect size tolerance.

Experiments ignored for regressions

Regressions in experiments with settings containing erratic: true are ignored.

perf	experiment	goal	Δ mean %	Δ mean % CI
➖	file_to_blackhole	% cpu utilization	+1.05	[-0.14, +2.24]

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI
➖	tcp_syslog_to_blackhole	ingress throughput	+13.01	[-9.15, +35.16]
➖	file_to_blackhole	% cpu utilization	+1.05	[-0.14, +2.24]
➖	idle	memory utilization	+0.47	[+0.43, +0.51]
➖	file_tree	memory utilization	+0.33	[+0.24, +0.42]
➖	uds_dogstatsd_to_api_cpu	% cpu utilization	+0.12	[-2.71, +2.96]
➖	uds_dogstatsd_to_api	ingress throughput	+0.00	[-0.20, +0.20]
➖	trace_agent_json	ingress throughput	-0.00	[-0.01, +0.01]
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.00	[-0.03, +0.03]
➖	trace_agent_msgpack	ingress throughput	-0.01	[-0.02, +0.00]
➖	otel_to_otel_logs	ingress throughput	-0.04	[-0.41, +0.33]
➖	process_agent_standard_check_with_stats	memory utilization	-0.16	[-0.20, -0.11]
➖	basic_py_check	% cpu utilization	-0.31	[-2.64, +2.02]
➖	process_agent_standard_check	memory utilization	-0.35	[-0.40, -0.29]
➖	process_agent_real_time_mode	memory utilization	-1.08	[-1.13, -1.04]
➖	pycheck_1000_100byte_tags	% cpu utilization	-2.24	[-6.98, +2.50]

Explanation

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

1. Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.

2. Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.

3. Its configuration does not mark it "erratic".

[alopezz]

/merge

[dd-devflow]

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