Add self-relation support when relationsDepthLimit is set

[dmythro]

The simplest way I found to allow self-relations securely (avoiding infinite depth etc), without breaking anything else or introducing extra configuration.

Issue: #38

[Copilot]

Pull Request Overview

This PR adds support for self-relations (tables referencing themselves) when a relationsDepthLimit is configured. Previously, self-relations were blocked by the usedTables check regardless of depth limit settings.

• Modified the condition in generateSelectFields to allow self-relations when relationsDepthLimit is set
• Added parentId column to Posts table schema for self-referencing functionality
• Added comprehensive tests covering both default behavior (blocking self-relations) and new behavior (allowing self-relations with depth limits)

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/util/builders/common.ts	Updated logic to conditionally apply usedTables check based on relationsDepthLimit setting
tests/schema/pg.ts	Added parentId column and parent/replies relations for self-referencing Posts
tests/pg.test.ts	Added extensive test coverage for self-relation behavior with and without depth limits

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