Add count queries

[dmythro]

In order to not introduce breaking changes on list responses, Count queries are added on the same level where <table>Single is generated as <table>Count. They use the same where filters as list, but return item count number only.

[Copilot]

Pull Request Overview

This PR adds count query functionality to the GraphQL schema by introducing new count resolvers for each table. The implementation provides basic count queries and count queries with filtering capabilities across all database adapters (SQLite, PostgreSQL, and MySQL).

• Adds executeCountQuery utility function in common.ts with fallback support for different database implementations
• Implements generateSelectCount function in each database adapter to create count resolvers
• Adds comprehensive test coverage for count queries across all database adapters

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/util/builders/common.ts	Adds executeCountQuery utility function with modern $count API and fallback to manual count queries
src/util/builders/sqlite.ts	Implements generateSelectCount function and integrates count queries into SQLite schema generation
src/util/builders/pg.ts	Implements generateSelectCount function and integrates count queries into PostgreSQL schema generation
src/util/builders/mysql.ts	Implements generateSelectCount function and integrates count queries into MySQL schema generation
tests/sqlite.test.ts	Adds test cases for basic count, filtered count, and posts count queries for SQLite
tests/sqlite-custom.test.ts	Adds test cases for custom count queries in SQLite custom schema
tests/pg.test.ts	Adds test cases for basic count, filtered count, and posts count queries for PostgreSQL
tests/pg-custom.test.ts	Adds test cases for custom count queries in PostgreSQL custom schema
tests/mysql.test.ts	Adds test cases for basic count, filtered count, and posts count queries for MySQL
tests/mysql-custom.test.ts	Adds test cases for custom count queries in MySQL custom schema

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