fix: properly parse PNG iTXt chunks per specification (#8530)

## Summary
Fixes PNG iTXt chunk parsing to comply with the PNG specification.

## Problem
The current iTXt parser incorrectly reads the text content immediately
after the keyword null terminator, but iTXt chunks have additional
fields:
- Compression flag (1 byte)
- Compression method (1 byte)
- Language tag (null-terminated)
- Translated keyword (null-terminated)
- Text content

This caused PNGs that correctly follow the spec to fail loading with
JSON parse errors due to leading null bytes.

## Solution
Skip the compression flag, method, language tag, and translated keyword
fields before reading the text content.

Fixes #8150

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8530-fix-properly-parse-PNG-iTXt-chunks-per-specification-2fa6d73d36508189bef4cc5fa3899096)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: github-actions <github-actions@github.com>

browser_tests/tests/loadWorkflowInMedia.spec.ts

@@ -16,6 +16,7 @@ test.describe(
       'no_workflow.webp',
       'large_workflow.webp',
       'workflow_prompt_parameters.png',
+      'workflow_itxt.png',
       'workflow.webm',
       // Skipped due to 3d widget unstable visual result.
       // 3d widget shows grid after fully loaded.