Shape getColumns rows through named records #208

Goal

Replace the positional shaping in getColumns with named records. The 74-line method rebuilds 24 Col entries on every call and reads nine row positions by magic index.

Depends on

#207. Same file.

Pin

LibsqlDatabaseMetaDataTest.getColumnsReportsDeclaredTypesSizesNullabilityAndAutoIncrement asserts all 24 columns for four rows. The xerial DBMetaDataTest adds generated columns, precision and scale, and column order.

Scope

• Lift the 24 Col entries to a static constant beside FOREIGN_KEY_COLUMNS.
• Add a record for the pragma row and one for the JDBC row, with fromRow and toRow.
• Keep NUM_PREC_RADIX as the literal 10, not DEFAULT_DECIMAL_DIGITS.
• Keep BUFFER_LENGTH and CHAR_OCTET_LENGTH at 2_000_000_000.

Preserve

• IS_AUTOINCREMENT stays primaryKey and the grammar result. IS_GENERATEDCOLUMN stays hidden == 2 or 3.
• NULLABLE derives from notnull only, never from the primary key.
• REMARKS stays NULL, and the SQL_* and SCOPE_* columns keep their current values.

Acceptance

• getColumns shapes rows through named accessors, with no positional values.get(n) left.
• LibsqlDatabaseMetaData.java is under 900 lines.
• ./mvnw -pl libsql-jdbc -am test green with no assertion edited.
• ./mvnw spotless:check green.