perf: vectorize standard basis construction

[09Catho]

Summary

• replace the Python-level standard-basis construction loop with numpy.eye
• preserve flattened and column-vector output shapes
• broaden exact-output coverage across dimensions 1, 2, and 5

Performance

Measured locally with Python 3.13 and NumPy through the project uv environment:

Dimension	Previous	Vectorized	Speedup
32	1313.3 us/call	16.8 us/call	78.0x
128	18848.0 us/call	58.8 us/call	320.4x

The benchmark also asserted np.array_equal between the previous and new outputs.

Validation

• uv run pytest toqito/matrices/tests -q (143 passed)
• uv run ruff check toqito/matrices/standard_basis.py toqito/matrices/tests/test_standard_basis.py
• uv run ruff format --check toqito/matrices/standard_basis.py toqito/matrices/tests/test_standard_basis.py
• git diff --check

Closes #1887

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[vprusso]

Thanks, and welcome to toqito! Confirmed the np.eye version matches the previous output exactly in both flatten modes across dimensions, and the parametrized exact-equality tests are a nice improvement over the originals. Big speedup too. Merging.