tests: add conformance tests for `lib/trie`

## Issue summary

### Context

From @lileth on 2021-12-15:

> im wondering if we should add conformance tests or something for some of the packages (eg. trie), we don't really have those and issues will only be caught in CI when pushed to staging

> tests to make sure our implementation matches substrate's, the polkadot-tests repo by w3f has some tests there already, but if we broke our code it would require them pulling latest gossamer and telling us we broke it haha

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