feat: add constants/float16/inv-pi

[Amansingh0807]

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Resolves #{{TODO: add issue number}}.

Description

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This pull request:

• add constants/float16/inv-pi

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This pull request has the following related issues:

• #{{TODO: add related issue number}}

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Coverage Report

Package	Statements	Branches	Functions	Lines
constants/float16/inv-pi	$\color{green}48/48$ $\color{green}+100.00%$	$\color{green}1/1$ $\color{green}+100.00%$	$\color{green}0/0$ $\color{green}+100.00%$	$\color{green}48/48$ $\color{green}+100.00%$

The above coverage report was generated for the changes in this PR.

[Amansingh0807]

Hi @Neerajpathak07,
While working on inv-two-pi across all precisions, I also noticed that inv-pi currently exists only in my open PR for float16.
If you think it makes sense, I can add the float32 and float64 versions as well once the float16 PR is merged or get review.
Just wanted to check before proceeding.

[Neerajpathak07]

It's better to hold those for a while till we can get the PR's on inv-two-pi in.

[Neerajpathak07]

One thing that's on top of my mind is that whether this package is necessary and if so which packages would we be needing this constant for.

[Amansingh0807]

Thanks for the clarification, @Neerajpathak07!

Regarding the usefulness of inv-pi:

1/π appears quite frequently in numerical code, especially in :

• probability distributions (e.g., Cauchy pdf: 1/(π * (1 + x²))),
• Fourier/signal-processing normalizations, and
• several special-function kernels where π or 2π factors appear in denominators.

Having a dedicated constant avoids repeated divisions, ensures consistent rounding across precisions, and keeps the API parallel to existing constants like two-pi, and half-pi.

But yes, I am happy to wait until the inv-two-pi PRs land before proceeding further.