docs: fix forward-result comment in differentiable tensors example

[nv-slang-bot]

Summary

Standalone docs correction. In docs/src/tensors/differentiable.rst, "Basic Example: Polynomial Function", the Python block's forward-result comment showed the wrong values.

• Wrong: # [9., 27., 53., 87.]
• Right: # [9., 23., 41., 63.]

The example evaluates 2*x^2 + 8*x - 1 over x = [1, 2, 3, 4]:

• x=1 → 2 + 8 − 1 = 9
• x=2 → 8 + 16 − 1 = 23
• x=3 → 18 + 24 − 1 = 41
• x=4 → 32 + 32 − 1 = 63

The backward comment # [12., 16., 20., 24.] (= 4x + 8) is already correct and is left unchanged.

5-bullet summary

• Status: Docs-only one-line fix; pushed, opened as draft PR.
• Link: this PR.
• Verdict: Stale forward-result comment corrected to match the arithmetic and the reporter's own output.
• Next-action: Human maintainer to review and promote from draft.
• Blocker: None.

Docs-only; no code, no test.

_{🤖 Generated by an automated SlangPy coworker — may be inaccurate. A human maintainer should verify.}

[jhelferty-nv]

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