Check if input value is integer before conversion

[stellabelin]

E.g. if you run set_peripheral_compartments(model, 1.5) pharmr will convert this with as.integer making it into 1, however this should raise.

[stellabelin]

If inputting something that cannot be converted to an integer such as a string (as.integer('a')) the variable will be NA of class integer. When this is then run through reticulate, this will be converted to the lowest negative value. Example:

> reticulate::r_to_py(as.integer('a'))
-2147483648

This can lead to strange edge cases, such as when using set_peripheral_compartments it gets stuck. pharmr should catch this before trying to convert values to integers.

[rikardn]

I guess we should only allow integer and numeric that are exactly integers. Everything else should raise.