Tracker for hotspots to move to cython

Summary

We have some hotspots in the code base, that are stable and "leafs" in the codebase.

We should convert them to cython when it makes sense.

This ticket is to track the spots in the code that are potential candidates and coordinate the work made in that regard.

Candidates

• utils.url_directory_name
• _loader.types.Dependency
• _loader.loadelement._extract_depends_from_node
• _loader.loader.valid_chars_name
• element.Element.dependencies
• _loader.Loader._check_circular_deps
• _loader.Loader._sort_dependencies
• node._assert_symbole_name (needs inlining of the valid_chars)

Not necessarily hot, but easy to convert now

• _loader.Loader._collect_element
• _options.optionpool
• _yaml.FileInfo use __cinit__ instead of __init__
• _yaml.ProvenanceInformation use __cinit__ instead of __init__

Other Cython-related optimizations

• Stop allowing negative indexing or lists in Cython
• Use @cython.freelist() for heavily used extension types

Feel free to edit or comment on this issue to add more methods that should get cythonized.