test: add unit tests for pet-venv crate (Fixes #389)

[karthiknadig]

Add 4 new unit tests to pet-venv (17 total, up from 13):

• try_from without prefix derives from executable path
• try_from uses version from PythonEnv when provided
• try_environment_from_venv_dir with no prompt in pyvenv.cfg
• is_venv detects pyvenv.cfg via executable parent

Fixes #389

[github-actions]

Test Coverage Report (Linux)

Metric	Value
Current Coverage	75.7%
Base Branch Coverage	75.6%
Delta	.1% ✅

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Coverage increased! Great work!

[github-actions]

Performance Report (Linux) ✅

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta	Change
Server Startup	1ms	1ms	1ms	0ms	0%
Full Refresh	54ms	102ms	56ms	-2ms	0%

Results based on 10 iterations. P50 = median, P95 = 95th percentile.

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Legend

• 🚀 Significant speedup (>100ms faster)
• ✅ Faster than baseline
• ➖ No significant change
• 🔺 Slower than baseline (>100ms)
• ⚠️ Significant slowdown (>500ms)

[github-actions]

Performance Report (macOS)

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta
Server Startup	103ms	638ms	107ms	-4ms
Full Refresh	180ms	38579ms	198ms	-18ms

Results based on 10 iterations. P50 = median, P95 = 95th percentile.

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Legend

• 🚀 Significant speedup (>100ms faster)
• ✅ Faster than baseline
• ➖ No significant change
• 🔺 Slower than baseline (>100ms)
• ⚠️ Significant slowdown (>500ms)

[github-actions]

Performance Report (Windows) ➖

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta	Change
Server Startup	9ms	12ms	9ms	0ms	0%
Full Refresh	168ms	368ms	153ms	15ms	9.8%

Results based on 10 iterations. P50 = median, P95 = 95th percentile.

---

Legend

• 🚀 Significant speedup (>100ms faster)
• ✅ Faster than baseline
• ➖ No significant change
• 🔺 Slower than baseline (>100ms)
• ⚠️ Significant slowdown (>500ms)

[github-actions]

Test Coverage Report (Windows)

⏳ Coverage analysis in progress...

This comment will be updated with results when the analysis completes.