Add SQL Export Format to `lino pull` Command

[youen]

As part of the effort to support multiple export formats in the lino pull command, this sub-task focuses on implementing SQL format support (#309).

Tasks:

• Implement SQL generation logic that converts the pulled data into SQL INSERT statements.
• Add a --format sql option to the lino pull command.
• Ensure that the SQL export can handle all existing lino pull flags and options (e.g., --limit, --filter, --where).
• Add unit and integration tests to verify SQL generation accuracy.
• Update the documentation with examples of how to use the SQL export format.

Acceptance Criteria:

• The lino pull command generates valid SQL scripts that can be executed to initialize a test database.
• All relevant lino pull flags and options are compatible with the SQL export format.
• Documentation is updated with SQL format usage examples.