Add .default methods for the int_*() generics

[hfrick]

Give the int_*() generics a .default() method with a nicer error message

rsample/tests/testthat/_snaps/bootci.md

Lines 112 to 132 in bdf12e1

	Code
	int_pctl(vfold_cv(mtcars))
	Condition
	Error in `UseMethod()`:
	! no applicable method for 'int_pctl' applied to an object of class "c('vfold_cv', 'rset', 'tbl_df', 'tbl', 'data.frame')"
	---
	Code
	int_t(vfold_cv(mtcars))
	Condition
	Error in `UseMethod()`:
	! no applicable method for 'int_t' applied to an object of class "c('vfold_cv', 'rset', 'tbl_df', 'tbl', 'data.frame')"
	---
	Code
	int_bca(vfold_cv(mtcars))
	Condition
	Error in `UseMethod()`:
	! no applicable method for 'int_bca' applied to an object of class "c('vfold_cv', 'rset', 'tbl_df', 'tbl', 'data.frame')"