BUG: asarray: fix default format for SparseArray input

[lucascolley]

What type of PR is this? (check all applicable)

• 💾 Refactor
• 🪄 Feature
• 🐞 Bug Fix
• 🔧 Optimization
• 📚 Documentation
• 🧪 Test
• 🛠️ Other

Checklist

• Code follows style guide
• Tests added
• Documented the changes

---

fixes

In [16]: sparse.asarray(sparse.GCXS.from_numpy(np.empty(0)))
Out[16]: <COO: shape=(0,), dtype=float64, nnz=0, fill_value=0.0>

[hameerabbasi]

Amazing, thanks @lucascolley!

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will degrade performance by 19.94%

_{Comparing lucascolley:asarray-default (ac5785d) with main (67be471)}

Summary

❌ 1 regressed benchmark
✅ 339 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	test_index_fancy[side=100-rank=1-format='coo']	748.3 µs	934.6 µs	-19.94%