feat: add no-single-property-require ESLint rule

[Planeshifter]

Resolves stdlib-js/metr-issue-tracker#664.

Description

What is the purpose of this pull request?

This pull request:

• adds a new custom ESLint rule no-single-property-require which flags module-scope var x = require( '...' ); declarations where the required binding is only ever used to access a single property (e.g., x.ndarray( ... ) everywhere) and suggests requiring the property directly (e.g., var x = require( '...' ).ndarray;), which reduces bundle sizes during ESM tree-shaking via named imports.
• registers the rule in the rules namespace and enables it as 'warn' in the stdlib ESLint configuration (existing violations exist across the codebase, so enabling as 'error' would break linting repo-wide; the rule can be promoted to 'error' in a follow-up once violations are cleaned up).
• disables the rule for test files (which intentionally require the package under test as a whole) and Markdown code blocks (which deliberately demonstrate namespace-style access).

Related Issues

Does this pull request have any related issues?

No.

Questions

Any questions for reviewers of this pull request?

• Is 'warn' the right initial severity, or should the rule start as 'error' with overrides?

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

• The rule uses ESLint scope analysis (sourceCode.getDeclaredVariables) to walk all references of a required binding, including references within nested closures.
• Bindings used "bare" anywhere (called directly, passed as argument, returned, exported, typeof), via computed access (x[ key ]), re-assigned, or mutated (x.foo = 1, delete x.foo, x.count++) are not flagged.
• Only module-scope (top-level) declarations are considered, per stdlib convention of placing require statements at the top of a module.
• The rule is report-only (no autofix): converting a method-style call (x.ndarray()) to a direct call changes the this context within the called function, so automatic rewriting is deliberately avoided.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

This PR was written primarily by Claude Code, modeled on the existing uppercase-required-constants and no-unnecessary-nested-functions rules; the approach and configuration decisions were reviewed and directed by myself.

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