[Pg-core]: add typed references to PostgreSQL columns

[tharropoulos]

TLDR

Add proper type tracking for PostgreSQL column references with optional/required distinction.

Change Summary

Added Features:

1. Typed References in PostgreSQL:
   • Added proper type information to references between columns
   • Implemented typed references property on columns to track reference relationship
   • Distinction between optional and required references based on notNull status

Code Changes:

1. In column-builder.ts:

   • Refactored BuildColumn type with conditional types to track reference relationships
   • Added reference type parameter to PgColumn generic interface
   • Added differentiation between optional and required references

2. In pg-core/columns/common.ts:

   • Made ReferenceConfig generic to preserve type of referenced column
   • Updated references() method to return enhanced type with reference information
   • Added references property to PgColumn class to store reference target
   • Set reference during foreign key setup in column creation

Tests:

1. In type-tests/pg/references.ts:
   • Added type tests to validate optional and required reference behavior
   • Verified correct type inference for both reference scenarios

Context

• This change improves the type safety of column references in PostgreSQL, allowing TypeScript to track the relationship between columns and providing better autocomplete and type checking for referenced columns (Getting references from a column in types #4387)