improve python management for free-threaded python (#10606)

* bump required pbs-installer version so that free-threaded Python uses a different directory for installation (cf frostming/pbs-installer#11)
* do not use an upper bound for pbs-installer because it uses calver
* do not complain that a python version is already installed when trying to install a free-threaded python with the same version
* list free-threaded python versions with a trailing "t"
* allow to request a free-threaded version with a trailing "t" instead of the command option
* add support for removing free-threaded python versions
* fix removing Python versions with patch version "0"