fix: Add TypeScript type definitions for Sequelize DataTypes (VECTOR, HALFVEC, SPARSEVEC)

[kai63001]

Problem

TypeScript users get type errors when using DataTypes.VECTOR(), DataTypes.HALFVEC(),
or DataTypes.SPARSEVEC() because the type definitions don't augment Sequelize's DataTypes.

Error: Property 'VECTOR' does not exist on type 'typeof DataTypes'

Solution

Added module augmentation in types/sequelize/index.d.ts to extend Sequelize's
DataTypes namespace with the vector types.

Changes

• Added VectorDataTypeConstructor, HalfvecDataTypeConstructor, SparsevecDataTypeConstructor interfaces
• Added module augmentation for sequelize to declare the types on DataTypes namespace
• Supports both DataTypes.VECTOR(3) and DataTypes.postgres.VECTOR(3)