fix: bump version to 0.7.0 and add scipy to cibuildwheel test-requires

[rappdw]

Summary

• Bump version from 0.6.1-dev to 0.7.0 in both pyproject.toml and meson.build
• Add scipy to test-requires in [tool.cibuildwheel] to prevent scipy from building from source in manylinux containers (no OpenBLAS available)
• Checked release.yml: cibuildwheel is already at v2.23.4 (no update needed)

Test plan

• Verify release workflow triggers correctly on v0.7.0 tag
• Confirm cibuildwheel import test passes with scipy available in test environment

🤖 Generated with Claude Code

[github-actions]

Package	Line Rate	Complexity	Health
.	68%	0	➖
core	92%	0	✔
reference	98%	0	✔
sparse	94%	0	✔
sparse.csgraph	58%	0	❌
types	100%	0	✔
util	67%	0	➖
Summary	73% (1489 / 2036)	0	➖

Minimum allowed line rate is 65%