Refactor mkthreadsafe to C++

[JCGoran]

The mkthreadsafe script is a bit hard to follow, and error-prone due to its heavy use of grep. This is an attempt at rewriting it in C++ using NMODL's AST abilities. This means that mkthreadsafe no longer depends on POSIX tooling, and is much more maintainable.

TODO:

• handle case when NEURON block is missing
• rewrite CMake code so mkthreadsafe is built even without NRN_ENABLE_CORENEURON=ON
• add tests

[sonarqubecloud]

Quality Gate passed

Issues
15 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.09%. Comparing base (967bf3a) to head (e443e6d).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3666   +/-   ##
=======================================
  Coverage   68.08%   68.09%           
=======================================
  Files         686      686           
  Lines      110904   110904           
=======================================
+ Hits        75508    75516    +8     
+ Misses      35396    35388    -8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[azure-pipelines]

✔️ e443e6d -> Azure artifacts URL

[github-actions]

✔️ e443e6d -> artifacts URL