feat: add @stdlib/ndarray/nans-like

[Planeshifter]

Description

This PR adds the @stdlib/ndarray/nans-like package, which creates an ndarray filled with NaN values having the same shape and data type as a provided input ndarray.

Key design decisions

• Restricted dtype support: Only floating-point and "generic" data types are supported (via dtypes('floating_point_and_generic')), as NaN is not defined for integer types. Attempting to use an integer dtype throws a TypeError.
• Complex NaN fill: For complex128 and complex64, fill(out, NaN) produces real=NaN, imag=0.0 — consistent with NumPy's behavior for np.full(..., np.nan, dtype=complex128).
• Pattern: Follows @stdlib/ndarray/ones-like exactly, substituting NaN as the fill value and restricting the dtype set accordingly.
• Namespace: Wired into @stdlib/ndarray alphabetically between mostlySafeCasts and ndarraylike2ndarray.

Files added/modified

• lib/node_modules/@stdlib/ndarray/nans-like/ — new package
  • lib/main.js — core implementation
  • lib/index.js — module entry point
  • package.json
  • test/test.js — 316 tests covering all dtypes, all option overrides, edge cases
  • examples/index.js
  • benchmark/benchmark.js and per-dtype size benchmarks
  • docs/repl.txt
  • docs/types/index.d.ts — TypeScript declarations using FloatingPointAndGenericDataType
  • docs/types/test.ts
  • README.md
• lib/node_modules/@stdlib/ndarray/lib/index.js — add nansLike to namespace
• lib/node_modules/@stdlib/ndarray/docs/types/index.d.ts — add nansLike type to namespace interface

Related Issues

Closes stdlib-js/todo#2771

Questions

None.

Other

• All 316 tests pass.
• This implementation was developed with AI assistance (Claude Code / claude-sonnet-4-6).

Checklist

• I have read the contributing guidelines.
• I have followed the code style guidelines.
• The implementation is based on an existing analogous package (@stdlib/ndarray/ones-like).
• Tests cover all supported dtypes, all option overrides, error cases, and edge cases (zero-dim, empty arrays).
• AI assistance disclosure: this PR was generated with Claude Code (claude-sonnet-4-6).

https://claude.ai/code/session_01THn379nEWg1u7YggFFBuFQ

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Generated by Claude Code

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[kgryte]

This was also completed earlier this evening, but the diff between what I pushed and this PR is instructive. The tests were not quite right. The use of a real-valued NaN was incorrect and inconsistent with ndarray/base/nans. And some spurious notes.

I'll go ahead and close.