fix: support full 64-bit integer range for number inputs in int64/ctor

[impawstarlight]

Resolves none.

Description

What is the purpose of this pull request?

This pull request:

• Lifts the restriction on number arguments to the Int64 constructor to allow unsafe integers of magnitude upto 2^64-1.

Related Issues

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No.

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@stdlib-js/reviewers

[impawstarlight]

Depends on #15475

[kgryte]

@impawstarlight Should we go ahead and add int64/base/bigint2words?

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
number/int64/ctor	$\\color{red}594/676$ $\\color{green}+0.00\\%$	$\\color{red}48/52$ $\\color{green}+0.00\\%$	$\\color{red}9/11$ $\\color{green}+0.00\\%$	$\\color{red}594/676$ $\\color{green}+0.00\\%$

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

[kgryte]

LGTM