test: expand pipenv locator coverage

[karthiknadig]

Adds 19 new unit tests to pet-pipenv (from 5 to 24 total).

New coverage:

• get_pipenv_virtualenv_dirs(): WORKON_HOME, XDG_DATA_HOME, ~/.local/share/virtualenvs, ~/.venvs, ~/.virtualenvs, empty/non-existent directories
• get_virtualenvs_dir(): WORKON_HOME preference, platform defaults, none case
• is_pipenv_from_project(): prefix-based, exe-path derivation, missing Pipfile
• is_pipenv(): plain venv rejection
• get_pipenv_project(): .project file reading, none case
• is_in_pipenv_centralized_dir(): prefix derivation from executable, non-derivable prefix
• Locator metadata validation

Fixes #389

[github-actions]

Test Coverage Report (Linux)

Metric	Value
Current Coverage	75.5%
Base Branch Coverage	74.9%
Delta	.6% ✅

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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	47ms	90ms	57ms	-10ms	-10.0%

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	94ms	600ms	57ms	37ms
Full Refresh	157ms	35736ms	130ms	27ms

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)

Metric	Value
Current Coverage	72.44%
Base Branch Coverage	71.72%
Delta	0.72% ✅

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Coverage increased! Great work!

[github-actions]

Performance Report (Windows) ✅

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta	Change
Server Startup	9ms	11ms	9ms	0ms	0%
Full Refresh	133ms	373ms	147ms	-14ms	-9.5%

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)