Results 3 issues of Ski

## About - Wrap each tree creation into MemoryPool: concept borrowed [from C++ solution in here](https://benchmarksgame-team.pages.debian.net/benchmarksgame/program/binarytrees-gpp-7.html). - Remove tree-walking Tree.deinit, as pool.deinit() already deallocates all memory - Zig tests show...

I think nested query statements gives much better readability compared to appends: Let' say I have helpers ```js function authorFilter(author) { return SQL`author=${author}`; } function nameFilter(name) { return SQL`name=${name}`; }...