Diesel: Possible unaligned data access for implementations of `SqliteAggregate`

Summary

Diesel allows to register custom aggregate SQL functions for SQLite via the `SqliteAggregate` interface. To store an instance of the custom aggregate processor Diesel relied on the `sqlite3_aggregate_context` function provided by sqlite. This function doesn't provide any guarantees about alignment of the returned allocation, which in turn can lead to problems if the type implementing requires a special alignment, e.g. via a custom `#[align(x)]` attribute on the type implementing this trait. This affects any user of `SqliteAggregate` that registers the custom aggregate function with an SQLite connection, while using a non-standard alignment on the type implementing this trait. ## Mitigation The preferred mitigation to the outlined problem is to update to a Diesel version 2.3.8 or newer, which includes fixes for the problem. ## Resolution Diesel now allocates the corresponding memory on Rust side to get a correctly aligned allocation.