test: add Mac Command Line Tools locator coverage

[karthiknadig]

Extracts helper functions for path validation and adds 30 unit tests to pet-mac-commandlinetools (previously zero tests).

Key changes:

• Extract is_cmdlinetools_python_path(), is_macos_python_executable_name(), is_valid_framework_version_dir() helpers
• Tighten try_from() to reject non-Python executables (python3-config, idle3, etc.) that previously slipped through prefix-only matching
• 30 tests covering locator metadata, exe name validation, version dir validation, path matching (positive and negative), and cross-platform rejection

Fixes #389

[github-actions]

Test Coverage Report (Linux)

Metric	Value
Current Coverage	76.0%
Base Branch Coverage	75.6%
Delta	.4% ✅

---

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	53ms	299ms	53ms	0ms	0%

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]

Performance Report (macOS)

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta
Server Startup	104ms	623ms	85ms	19ms
Full Refresh	164ms	45059ms	175ms	-11ms

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	72.94%
Base Branch Coverage	72.49%
Delta	0.45% ✅

---

Coverage increased! Great work!

[github-actions]

Performance Report (Windows) ✅

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta	Change
Server Startup	9ms	11ms	11ms	-2ms	-18.2%
Full Refresh	124ms	1357ms	202ms	-78ms	-38.6%

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)