Convert to TypeScript with enhanced type safety and schema support

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This PR completes the TypeScript conversion of the PostgreSQL query builder, building upon the draft work in PR #2. The implementation provides full type safety while maintaining complete backward compatibility with existing JavaScript usage.

Key Features

🔧 Complete TypeScript Implementation

All functionality from the original JavaScript version has been ported to TypeScript with proper type annotations:

import QueryBuilder from '@bigbadweb/postgres-query-builder';

const builder = QueryBuilder();
const query = builder
  .select('u.name', 'user_name')
  .from('users', 'u')
  .whereEquals('u.status', 'active')
  .whereIsNotNull('u.email')
  .sql();

📋 Schema-Aware Type Safety (Drizzle-like)

Optional schema definitions provide compile-time type safety for table and column references:

interface MySchema extends SchemaDefinition {
  users: {
    id: 'number';
    email: 'string';
    name: 'string';
    is_active: 'boolean';
  };
}

const builder = QueryBuilder<MySchema>();
// TypeScript will now provide intellisense and type checking for column names

🐛 Bug Fixes

• Fixed critical bug in page() method where params.push() was called without arguments
• Fixed MySQL dialect support to properly use ? placeholders instead of $1, $2...
• Added dynamic dialect detection instead of compile-time constants

📦 Missing Method Implementation

Added several methods that were missing from the draft TypeScript version:

• whereNull(), whereIsNull(), whereIsNotNull() for NULL checking
• selectDistinctOn() with groupClause parameter support
• _selectMulti() for array-based column selection
• raw_join() for custom join clauses
• rangeFilterMultiColumn() and betweenColumnValuesMulti() for advanced filtering
• matchEmpty parameter support in array filtering
• customResultsFunc parameter in findMany()

🔄 Backward Compatibility

The TypeScript version maintains full compatibility with existing JavaScript codebases:

// Existing JavaScript code continues to work unchanged
const QueryBuilder = require('@bigbadweb/postgres-query-builder');
const builder = QueryBuilder();

🏗️ Build System

• Complete TypeScript build configuration with declaration file generation
• Updated package.json with proper TypeScript entry points
• Automated build process with npm run build
• Comprehensive test coverage

Migration Guide

For JavaScript Users

No changes required - existing code continues to work without modification.

For TypeScript Users

// Basic usage (no schema)
import QueryBuilder from '@bigbadweb/postgres-query-builder';
const builder = QueryBuilder();

// Schema-aware usage
import QueryBuilder, { SchemaDefinition } from '@bigbadweb/postgres-query-builder';
interface MySchema extends SchemaDefinition { /* your schema */ }
const builder = QueryBuilder<MySchema>();

The implementation now provides a modern, type-safe development experience while preserving all existing functionality and maintaining backward compatibility.

Fixes #3.

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