Affected: npm: liquidjs

### Summary

A circular block reference in `{% layout %}` / `{% block %}` causes an infinite recursive loop, consuming all available memory (~4GB) and crashing the Node.js process with `FATAL ERROR: JavaScript heap out of memory`. This allows any user who can submit a Liquid template to perform a Denial of Service attack.

### Details

In `src/tags/block.ts`, during OUTPUT mode, each block looks up its render function from `ctx.getRegister('blocks')[this.block]`. When a block with name `a` is nested inside another block also named `a` in a child template, the inner block finds the outer block's render function and calls it. The outer block's templates contain the inner block again, creating infinite recursion with no termination condition.

Relevant code (`src/tags/block.ts`, `getBlockRender` method):

```typescript private getBlockRender (ctx: Context) { const { liquid, templates } = this const renderChild = ctx.getRegister('blocks')[this.block] const renderCurrent = function * (superBlock: BlockDrop, emitter: Emitter) { ctx.push({ block: superBlock }) yield liquid.renderer.renderTemplates(templates, ctx, emitter) ctx.pop() } return renderChild ? (superBlock: BlockDrop, emitter: Emitter) => renderChild( new BlockDrop( (emitter: Emitter) => renderCurrent(superBlock, emitter) ), emitter) : renderCurrent } ```

When `renderChild` exists (same-name block found), it calls `renderChild` which re-renders templates con…