Mycelia Test Coverage Expansion

Systematically expand test coverage for the Mycelia Julia package.

Prerequisites

1. Check for existing coverage files:

   find . -name "*.cov" -mtime -1 2>/dev/null
   

   If recent .cov files exist, use them to identify gaps without re-running.

2. Environment flags - ALWAYS enable these for accurate coverage:

   export MYCELIA_RUN_ALL=true
   export MYCELIA_RUN_EXTERNAL=true
   

   Coverage needs non-precompiled code for accurate line hits. Use --compiled-modules=no (matches ci/hpc/run_hpc_ci.sh).