Better function argument verification

[drkameleon]

Right now, we are verify function arguments by effectively embedding an ensure call. (more or less what I describe here: https://discord.com/channels/765519132186640445/829324913097048065/1309436123017117707)

The actual implementation is here: https://discord.com/channels/765519132186640445/829324913097048065/1309437688696537138

Given that we now (and for quite some time) store all this information in a Function value's .info field (see: https://github.com/arturo-lang/arturo/blob/master/src/vm/values/types.nim#L209-L213), we could use that to check the parameters, before execution... e.g. here: https://github.com/arturo-lang/arturo/blob/master/src/vm/exec.nim#L342