feat: add react-x/no-unnecessary-key, closes #950

[Rel1cx]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• Test
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• I have added a convincing reason for adding this feature, if necessary

Other information

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Project	Deployment	Preview	Comments	Updated (UTC)
eslint-react	Ready	Preview	Comment	Aug 26, 2025 8:42pm

[Copilot]

Pull Request Overview

This PR introduces a new ESLint rule no-unnecessary-key that prevents unnecessary key props on JSX elements when rendering lists. The rule identifies cases where keys are placed on child elements instead of the top-level element returned from array maps.

• Adds the new rule implementation with proper detection logic for unnecessary keys in map callbacks
• Includes comprehensive test coverage for various scenarios including nested elements and fragments
• Provides detailed documentation with examples of correct and incorrect usage

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/plugins/eslint-plugin/src/configs/all.ts	Adds the new rule to the "all" configuration
packages/plugins/eslint-plugin/README.md	Updates branch references in contributing guidelines
packages/plugins/eslint-plugin-react-x/src/rules/no-unnecessary-key.ts	Implements the core rule logic for detecting unnecessary keys
packages/plugins/eslint-plugin-react-x/src/rules/no-unnecessary-key.spec.ts	Provides comprehensive test cases for the rule
packages/plugins/eslint-plugin-react-x/src/rules/no-unnecessary-key.mdx	Documents the rule with examples and usage guidelines
packages/plugins/eslint-plugin-react-x/src/plugin.ts	Registers the new rule in the plugin
packages/plugins/eslint-plugin-react-x/src/configs/recommended.ts	Removes commented-out rules (cleanup)
packages/plugins/eslint-plugin-react-x/src/configs/recommended-type-checked.ts	Removes commented-out rule (cleanup)
apps/website/content/docs/rules/overview.mdx	Adds rule to documentation table
apps/website/content/docs/rules/meta.json	Includes rule in metadata

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