feat: add constants/float16/max-safe-nth-fibonacci

[sagar7162]

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This pull request:

• adds constants/float16/max-safe-nth-fibonacci

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Coverage Report

Package	Statements	Branches	Functions	Lines
constants/float16/max-safe-nth-fibonacci	$\color{green}49/49$ $\color{green}+0.00%$	$\color{green}1/1$ $\color{green}+0.00%$	$\color{green}0/0$ $\color{green}+0.00%$	$\color{green}49/49$ $\color{green}+0.00%$

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[sagar7162]

@kgryte
I am trying to clarify two different limits when computing Fibonacci numbers in IEEE-754 floating-point formats. One limit is representability: the largest index (n) for which the exact integer (F_n) can still be represented in a given format (e.g., float16 allows exact representation up to (F_{24})). The other limit is the iterative recurrence limit: when computing the sequence directly in the same float format using (F_{n+1}=F_n+F_{n-1}), (F_{23})) and (F_{22})) cant be represented accurately even though it is possible to represent (F_{24})). So if we consider this approach, then the limit comes to 18.
Could you please explain this distinction formally and outline the recommended approach for obtaining accurate Fibonacci numbers when restricted to low-precision formats?

[sagar7162]

@kgryte I have updated the values as per your suggestions kindly review the changes.