[Clarity-4] Implement contract post-conditions

[obycode]

Implements contract post-conditions as described in #6396 and SIP PR stacksgov/sips#218.

[obycode]

In implementing this, I'm wondering if it might be better to make a small change to the with-nft allowance. Currently, it is:

(with-nft contract-id:principal token-name:(string-ascii 128 identifier:T)

I'm wondering if it makes more sense to change that to allow a list of identifiers:

(with-nft contract-id:principal token-name:(string-ascii 128 identifier:(list T 128))

This would allow the list to be built within the code and then passed to a single allowance expression for each NFT.

[obycode]

Remaining work is to handle the with-stacking allowances, but the rest of this can be reviewed now.

[obycode]

Remaining tasks now are:

• Testing stacking allowances
• Decide on event to emit for allowance violations and add it
• Test rollback on allowance violation

[hstove]

LGTM! Mainly I see that you have some unwritten integration test TODOs, but otherwise everything looks really well tested.

[hstove]

I know you check the args length above, but do we want to move away from index access even in situations like this?

[obycode]

Sure, I can update that and make them return a CheckerImplementationFailure error.

[obycode]

610c421

[obycode]

LGTM! Mainly I see that you have some unwritten integration test TODOs, but otherwise everything looks really well tested.

Thanks @hstove! I actually forgot about those TODOs I had at the bottom. The remaining tests I planned to add were:

1. Replicate the existing checks in check_with_stacking_allowances but with calls to stack-stx instead of delegate-stx
2. Duplicate check_restrict_assets_rollback but using as-contract?

Do you see any others that should get added?

[obycode]

@hstove TODOs resolved, additional tests added, and merge conflicts resolved.