This patch update the `EventCacheStore` trait to:
1. rename `reload_linked_chunk` into `load_all_chunks` and put this
method behind `#[cfg(test)]` so that it is removed from the public API,
2. add `load_last_chunk`,
3. add `load_previous_chunk`.
These 2 new methods are implemented inside the `MemoryStore` (with its
real implementation in the `RelationalLinkedChunk`), but `todo!()` are
added for the SQLite implementation.
Ivan Enderlin
334c66b0a0