docs(spark): Correct Spark memory model and fix post metadata

[DIYA-bot]

This commit refines the "Spark Architecture Explained" blog post, addressing a major technical inaccuracy and cleaning up frontmatter metadata.

Key changes:

Fix (Memory Model): Rewrites the "Memory Management" section to accurately describe the modern Unified Memory Model used since Spark 1.6. This removes the outdated and incorrect description of the old static 60/20/20 memory split.

1.Fix (Frontmatter): Deletes the entire commented-out meta: block, which contained incorrect placeholder content about DeepMind and MERN stack.

2.Chore (Frontmatter): Removes the empty canonical_url key.

3.Style (Code): Adds the scala language specifier to code blocks to enable proper syntax highlighting.

4.Style (Accessibility): Improves the alt text for the architecture diagram for better accessibility.

Description

Fixes # (issue)

Type of Change

• New feature (e.g., new page, component, or functionality)
• Bug fix (non-breaking change that fixes an issue)
• UI/UX improvement (design, layout, or styling updates)
• Performance optimization (e.g., code splitting, caching)
• Documentation update (README, contribution guidelines, etc.)
• Other (please specify):

Changes Made

Dependencies

• List any new dependencies or tools required for this change.
• Mention any version updates or configurations that need to be considered.

Checklist

• My code follows the style guidelines of this project.
• I have tested my changes across major browsers and devices
• My changes do not generate new console warnings or errors .
• I ran npm run build and attached screenshot(s) in this PR.
• This is already assigned Issue to me, not an unassigned issue.