Fix #1: cross-platform health check + Fix #5: independent log parser test fixtures

[cashmeout2313]

Fixes #1

Changes

tools/health_check.py — Cross-platform health check

• Added fallback paths for check_memory_usage() on non-Linux:
  1. macOS: uses vm_stat + pagesize via subprocess
  2. Any platform: tries psutil if available
  3. Gracefully returns WARNING when no mechanism works
• Replaced check_load_average() direct /proc/loadavg read with
  os.getloadavg() (cross-platform: Linux, macOS, BSD), falling
  back gracefully if unavailable
• All original Linux /proc paths retained as primary with
  try/except fallback chain

tools/tests/ — Independent log parser test fixtures

Closes #5

New tools/tests/ package with hand-crafted fixture files (not
generated by parser code):

• fixtures/json_logs.log — 15 JSON-structured log entries with
  various severity levels and key schemas (timestamp/time/@timestamp,
  level/severity/lvl, service/logger/app)
• fixtures/nginx_access.log — 15 Nginx combined-format access log
  entries with 2xx/4xx/5xx status codes
• fixtures/plain_text.log — 15 timestamped log entries with
  [service] LEVEL: format
• fixtures/syslog_messages.log — 15 syslog-formatted messages
  from kernel, sshd, dockerd, kubelet, postgres, nginx, etc.

Test files:

• test_log_parsers.py — 28 test cases across 4 test classes
  validating JSON, Nginx, plain-text, and syslog parsing against
  the known-correct fixture data
• test_health_check.py — 2 smoke tests for the health check return
  shape

All 30 tests pass.