feat: add blas/ext/base/dcartesian-power

[headlessNode]

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Resolves stdlib-js/metr-issue-tracker#174.

Description

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This pull request:

• add blas/ext/base/dcartesian-power

Related Issues

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This pull request has the following related issues:

• Resolves [RFC]: add blas/ext/base/dcartesian-power metr-issue-tracker#174

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Written primarily by Claude Code.

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Coverage Report

Package	Statements	Branches	Functions	Lines
blas/ext/base/dcartesian-power	$\color{green}422/422$ $\color{green}+100.00%$	$\color{green}24/24$ $\color{green}+100.00%$	$\color{green}4/4$ $\color{green}+100.00%$	$\color{green}422/422$ $\color{green}+100.00%$

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

[rautelaKamal]

Hey @headlessNode, excellent work on this feature! I reviewed the algorithm for generating Cartesian combinations via base-N conversion ((t % N, t / N)), it's very elegant.

One small edge case I noticed: len = stdlib_base_pow( N, k ) casts the result of the power operation into a CBLAS_INT. Because Cartesian powers grow extremely rapidly ((N^k)$), pow(N, k) could easily exceed the maximum positive value of a 32-bit signed integer (2,147,483,647).

If someone passes moderately large parameters (for example, N = 10 and k = 10), this will cause a silent integer overflow in C, whereas JS would just handle it as a double up to Number.MAX_SAFE_INTEGER.

Might be worth adding a safeguard check against 2147483647 before doing the loop so it explicitly bails instead of overflowing! Other than that edge case, the pointer arithmetic looks extremely solid. LGTM! 🚀