Tcl library dependencies

Any pkgIndex based libraries that are external to the project but which the project owners wish to distribute with the project and keep under source control.

These should generally be kept to a minimum 
- todo: dependency and version number tracking; along with the provision of a mechanism for the project end-users to update.



Platform subfolder structure (2026-07-22): the platform-named subfolders
follow the CANONICAL punkshell platform-dir names defined by the
punk::platform module (also surfaced as 'help platforms' in the punk shell)
plus the special 'allplatforms' folder for platform-independent libraries.
The boot machinery adds allplatforms plus the running platform's folder to
auto_path. Keep the set of subfolders here in sync with punk::platform's
supported/dormant records across BOTH vendorlib_tcl8 and vendorlib_tcl9.