[anveshachuri]

Closes #1055.

I picked up this issue because multiplication behaved asymmetrically depending on the order of the operands: a constant or one-term expression could multiply a multi-term expression in one direction but fail in the other. This change fixes that inconsistency while preserving the existing restriction on multiplying two multi-term expressions.

I added tests covering both multiplication orders for constant and one-term expressions on dense and sparse backends, while verifying that multi-term × multi-term still raises TypeError. The full test suite passes locally, excluding test/remote, which requires the oetc extra.

Checklist

• AI-generated content is marked (see AGENTS.md).
• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codspeed]

Merging this PR will not alter performance

✅ 181 untouched benchmarks
⏩ 181 skipped benchmarks¹

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_{Comparing anveshachuri:fix-constant-times-multiterm (201f26b) with master (9ad435d)}

Footnotes

1. 181 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[FabianHofmann]

@claude why is there a performance warning for the sparse path?