By default this parameter is filed by the namespace lft_userN. The old method, hard-wiring this parameter to lft_userN, had the defect of requiring to place libraries' namespacec in it *in advance*. The weak branch has always used such a parameter.

This simplifies the statements of all the toplevel typing theorem, and make them generic on the lifetime contexts, so that they can actually be used.

Other changes:
- Get rid of * spec pattern (deprecated in iris trunk)
- Make freeable_sz opaque (and simplifiy some proofs because of this)
- Refact option_as_mut and cell
- Prove lft_glb_acc, for gettings tokens of an intersections from tokens of its components
- Add some support for the = operator for ints in the proof mode

This reverts commit 04386c1c.

For consistency with how we call this elsewhere in Iris.