blog: Introduce blog post on long context models for code AI

[kukicado]

• Adds a new blog post exploring the benefits and tradeoffs of using long context window models in AI coding assistants like Cody
• Includes evaluation results comparing Cody's performance with 10k vs 1M token context windows
• Discusses the layered context architecture used to balance latency and coverage
• Outlines the road ahead for long context models in enterprise codebases

Before you merge this PR, please review the following:

Blog post

• [ ] Checked title case (This is correct. This Is Not Correct)
• [ ] Updated publishDate
• [ ] Updated authors
• [ ] Updated and checked slug
• [ ] Proofread for spelling and grammar errors
• [ ] Checked for consistent tone and voice throughout via Grammarly
• [ ] Ensured all links are working correctly
• [ ] Added relevant tags and categories
• [ ] Optimized meta description
• [ ] Included a new hero and social/OG image
• [ ] Uploaded images to Google Storage
• [ ] Formatted text for readability (headings, bullet points, etc.)
• [ ] Added image alt text
• [ ] Ran Markdown linter

Other

• [ ] This is not a blog post

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