lft is EqDecision and Countable

This adds EqDecision and Countable instances for lft to the lifetime logic's interface, analogously to the existing instances for atomic_lft.

These instances are used by RefinedRust (I overlooked them in my previous MR !38 (merged), and we only just noticed when porting to get rid of our fork of lambda-rust; sorry for the trouble!)

mentioned in merge request lgaeher/refinedrust-dev!67 (merged)

requested review from @jung

added 2 commits

• 1b2301d2 - move instances
• 5b4262a1 - add missing instances + group more sensibly

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resolved all threads

added 1 commit

• 1bffd356 - restore blank

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mentioned in commit 74bdf4e8

merged

Looks great, thanks :)

Great, thanks a lot! :)