feat(assert): add duration assertions

[Chemaclass]

🤔 Background

Adds assertions to verify command execution time, enabling performance testing directly in bashunit tests.

💡 Changes

• Add assert_duration to verify a command completes within a threshold (inclusive)
• Add assert_duration_less_than for strict less-than duration checks
• Add assert_duration_greater_than to verify minimum execution time
• Uses the framework's portable bashunit::clock::now for cross-platform millisecond measurement

[github-actions]

✅ Contributor Report

User: @Chemaclass
Status: Passed (13/13 metrics passed)

Metric	Description	Value	Threshold	Status
PR Merge Rate	PRs merged vs closed	93%	>= 30%	✅
Repo Quality	Repos with ≥100 stars	6	>= 0	✅
Positive Reactions	Positive reactions received	157	>= 1	✅
Negative Reactions	Negative reactions received	0	<= 5	✅
Account Age	GitHub account age	4569 days	>= 30 days	✅
Activity Consistency	Regular activity over time	108%	>= 0%	✅
Issue Engagement	Issues with community engagement	0	>= 0	✅
Code Reviews	Code reviews given to others	173	>= 0	✅
Merger Diversity	Unique maintainers who merged PRs	8	>= 2	✅
Repo History Merge Rate	Merge rate in this repo	89%	>= 0%	✅
Repo History Min PRs	Previous PRs in this repo	128	>= 0	✅
Profile Completeness	Profile richness (bio, followers)	100	>= 0	✅
Suspicious Patterns	Spam-like activity detection	0	N/A	✅

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_{Contributor Report evaluates based on public GitHub activity. Analysis period: 2025-02-21 to 2026-02-21}