Custom interestingness tests

[mrigger]

I looked into using SQLMin to reduce SQLite test cases. Most existing reducers like C-Reduce or Delta accept an "interestingness test", which essentially captures whether the reducer maintains a specific property as specified in a script. While for APOLLO, this is obviously the performance regression, I think it would be highly useful to also allow other interestingness tests (e.g., whether a logic bug is still reproduced). Judging from the source code and options, there is currently no way to specify other interestingness tests. Would it be possible to implement such an option?