The `best_index` implementation now returns a ResultCode along with the
IndexInfo. This allows it to signal specific outcomes, such as errors or
constraint violations. This change aligns better with SQLite’s xBestIndex
contract, where cases like missing constraints or invalid combinations of
constraints must not result in a valid plan.
Additional changes:
- Update IndexInfo documentation to clarify that constraint_usages must
have exact 1:1 correspondence with input ConstraintInfo array. The code
translating constraints into VFilter arguments heavily relies on this.
- Fix best_index implementation in test extension to comply with new
validation requirements by returning usage entry for each constraint
`BTreeTable::to_sql` makes us incompatible with SQLite by losing e.g. the original whitespace provided during the CREATE TABLE command.
For now let's fix our tests by regex-replacing every CREATE TABLE in
the entire repo to have exactly 1 space after the table name in the
CREATE TABLE statement.
