refactor: use constants/float64/nan in math/base/special/fibonacci

[puneetdixit200]

Resolves a part of #11743

Description

This pull request:

• Replaces inline 0.0 / 0.0 NaN generation in math/base/special/fibonacci with STDLIB_CONSTANT_FLOAT64_NAN.
• Adds @stdlib/constants/float64/nan as a manifest dependency for build, benchmark, and examples tasks.

Related Issues

This pull request has the following related issues:

• No.

Questions

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Other

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Verification

• make install-node-addons NODE_ADDONS_PATTERN='math/base/special/fibonacci'
• make EXAMPLES_FILTER='.*/math/base/special/fibonacci/.*' examples-c
• make BENCHMARKS_FILTER='.*/math/base/special/fibonacci/.*' benchmark-c
• make test TESTS_FILTER='.*/math/base/special/fibonacci/.*'

All package-specific checks passed.

Checklist

• Read, understood, and followed the contributing guidelines.

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

AI assistance helped identify the existing constant usage pattern and draft the small source/manifest refactor. The package-specific verification commands listed above were run locally.

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