* add new xfunctions

* add xfunction module and add cache decorator to bspl

* remove the explicit cache

* remove redundant integer type

* add add function for xfunction and switch to tuple method for the cache

* add test for poly module

* add test for indi module

* add test for indi module

* remove old scripts

* update install file

* update ci to python 3.10

* update typing

* add test for bspl

* separate the function evaluation and argument validation

* fix typo and import

* format XFunction as a function wrapper

* add constraint on integrals and recode add function

* add test for the XFunction.add

* change BundleXFunction to implement class method fun

* separate out the argument checking

* Add basis xfunction and convenient functions from bspl and poly

* add xspline class

* separate out cache clear function and auto clear in xspline

* change num_basis_funs from property to len fun

* add convenient import

* add tests for check args and function call of xfunction

* test basis xfunction

* add test for xspline

* add docstring for Bspl, Poly, Indi class

* add docstring to xfunction

* remove dependency on Optional

* add docstring to bspline function module

* add docstring to indicator function

* add docstring to poly class

* add docstring for the main xspline class

* change coefs to coef

* add installation and example to readme file

* add more examples

* add final example

* update badges

* add code of conduct

* add website documentation

* remove the images in the parent folder

* add gh actions to delopy docs