feat(migration): add methods for creating and adding columns, and enh…

[AxiosLeo]

…ance raw SQL execution

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Note

Adds addColumn and raw to the migration API, exports _initMigration, and introduces tests for these methods.

• Migration API:
  • Adds addColumn(tableName, columnName, options) to build column-addition SQL.
  • Adds raw(sql, values) to enqueue arbitrary SQL.
  • Exports internal helper _initMigration.
• Type Declarations (index.d.ts):
  • Declares addColumn with FieldType and CreateColumnOptions.
  • Declares raw(sql, values) on MigrationInterface.
  • Minor JSDoc adjustments for column creation.
• Tests:
  • New tests/migration.tests.js covering addColumn (various options) and raw (with values, empty, mixed).

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