test: add Panic and NotPanic

test: ErrorIs target and err both nil should pass

Go's builtin errors.Is returns true when both target and err are nil.

test: added variants of SliceContainsAll

assertions: make Error helper output more consistent

assertions: make Error helper output more consistent

ci: fix push vs pr

util: short-circuit dir entry loop

util: fix calls to crash with t

tests: make dir and file mode tests work on Windows

assertions: use os funcs in non-FS mode helpers

readme: notes for 1.9