SQLite: Design framework

[Mirko-von-Leipzig]

We want a slightly more ergonomic API than what rusqlite provides. This issue is for designing a solid baseline for this API such that we can "fall into the pit of success" when using it.

Some basic examples:

• We should never interact with raw Connections, only transactions.
• Statements should always be cached.
• We should distinguish between read and write transactions at the TYPE level.

The direction I would suggest is along the lines:

• Create tx and connection wrappers, never expose rusqlite directly.
• Create a read and write trait for reading/writing a single column
  • e.g. impl ToSql for AccountId + impl FromSql for AccountId
  • This is the database codec for our types

For improved ergonomics I would also suggest wrapping/extending the SQLite Row so that one can do things like:

row.get::<AccountId>(0)