Fix vmlab CI file length checks

[dannyota]

Summary

• remove the internal vmlab plan from tracked user documentation
• split SSE timestamp processing and vmlab script tests by topic
• keep code and user-doc length limits unchanged
• ignore local plans and worktrees in the length checker

Verification

• bash scripts/check-lengths.sh
• pytest --tb=short -q
• ruff check .
• ruff format --check .
• mypy splunkctl/
• installer mypy, Bash syntax, and shellcheck
• clean wheel build and install