SchemaReader: return the correct column definition for a composite primary key

[stefansaasen]

The PRAGMA table_info that is used to return the column definitions, returns one row for each defined column. The pk column contains:

... either zero for columns that are not part of the primary key, or the 1-based index of the column within the primary key).

See https://www.sqlite.org/pragma.html#pragma_table_info

Checking whether the pk column equals 1 only detects a single primary key and ignores other columns that are part of a composite primary key.

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• Write new tests for new functionality.
• Update documentation comments where applicable.

[nathanfallet]

LGTM, thanks!