docs(iavl): fix dead link in PERFORMANCE.md

[olegnechipa]

Description

Fixed a dead link to Golang performance analysis article by updating to current URL:

• Old: http://blog.ralch.com/tutorial/golang-performance-and-memory-analysis/ (returns 404)
• New: https://blog.ralch.com/articles/golang-performance-and-memory-analysis/

Verification

• Confirmed new URL is active and contains the original content

Checklist

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
  • Updated PERFORMANCE.md
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Reviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge PR #XYZ: [title]" (coding standards)