fix: improve Apex log detection robustness

[lukecotter]

📝 PR Overview

Improves Apex debug log detection to handle more real-world log formats — including logs with preamble text, missing API version prefixes, and logs that start with USER_INFO or EXECUTION_STARTED instead of the settings header. Also places the log duration decoration on the first valid log line rather than always line 0.

🛠️ Changes made

• Broaden ApexLogLanguageDetector to detect logs by EXECUTION_STARTED and USER_INFO lines, not just the settings header
• Make settings header regex optional for API version prefix (e.g. APEX_CODE,FINE;... without 64.0 prefix)
• Handle CRLF line endings in file-based detection (isApexLogFile)
• Remove firstLine from package.json language contribution (detection is now content-based)
• Add findFirstLogLine helper in LogTimingDecoration to place duration ghost text on the actual first log line
• Export APEXLOG_HEADER regex for reuse across modules
• Add comprehensive tests for isApexLogContent with 7 test cases covering standard, preamble, headerless, and negative scenarios

🧩 Type of change (check all applicable)

• 🐛 Bug fix - something not working as expected
• ✨ New feature – adds new functionality

🔗 Related Issues

N/A

✅ Tests added?

• 👍 yes - added ApexLogLanguageDetector.test.ts

📚 Docs updated?

• 🙅 not needed