upkeep: bump lifecycle from "experimental" to "stable"

[jdhoffa]

This package has about 95% test coverage, and is currently used in production.

@cjyetman do you think this package is ready to bump to "stable", and if not, are there specific tasks or issues that you think are blocking it from becoming so?

AB#10914

[cjyetman]

I have been questioning whether there should be both assert_valid_*() and is_valid_*() style functions for each data type it knows, one that errors or returns TRUE invisibly and one that returns TRUE or FALSE. That would be a rather large "interface" change. There are also a few significant things missing.

[cjyetman]

And some important things to fix like #69

[cjyetman]

also could consider making expect_*() style custom expectation functions for testing

[jdhoffa]

Depends on #74
Depends on #69