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	76.2%
Base Branch Coverage	75.6%
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	0ms	1ms	N/A%
Full Refresh	54ms	405ms	53ms	1ms	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	72ms	685ms	85ms	-13ms
Full Refresh	172ms	40254ms	175ms	-3ms

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	73.18%
Base Branch Coverage	72.49%
Delta	0.69% ✅

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Coverage increased! Great work!

[github-actions]

Performance Report (Windows) ✅

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta	Change
Server Startup	11ms	14ms	11ms	0ms	0%
Full Refresh	163ms	1603ms	202ms	-39ms	-19.3%

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)