greta messes up the arguments in backsolve/forwardsolve for non greta arrays

This is a 9yo bug of mine I just spotted.

The arguments to `greta::backsolve.default` and `greta::forwardsolve.default` (defined in order to make those funciton generic so we can have greta versions) are not passed through to the base functions:
https://github.com/greta-dev/greta/blob/main/R/functions.R#L810-L819

This means that when greta is loaded and either `backsolve()` or `forwardsolve()` are applied to an object that _isn't_ a greta array, the values of the `upper.tri` and `transpose` arguments they pass are silently ignored.

This tripped me up for hours, but I guess I deserve it since I created the bug.