Lightnode kv store

[cody-littley]

Why are these changes needed?

Creates an abstraction around level DB that allows it to be used by the light node without having too hard of a dependency on level DB.

Checks

• [x] I've made sure the lint is passing in this PR.
• [x] I've made sure the tests are passing. Note that there might be a few flaky tests, in that case, please comment that they are not relevant.
• Testing Strategy
  • [x] Unit tests
  • [ ] Integration tests
  • [ ] This PR is not tested :(