Improve XCM fuzzer (#6190)

* Add improved XCM fuzzer

* Add command for running a single input

* Add installation command

* Fix @m-cat's nit

* Add newline

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Add info about current directory in fuzzing README

* Update Cargo.lock

---------

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>