PHP 8

PHP 8 Upgrade

Added in new mixed type for generics
All functions should now have the ability to use named args
Everything is now making use of the nullsafe operator where appropriate
Constructor promoting us now used

Misc

[breaking] changed RopeNode changeValue renamed to updateValue to keep inline with other functions
[breaking] normalized the argument order and names of all functions, this should make everything feel more consistent
Updated all dependencies
Improved code coverage
Removed a few unreachable code paths