fix: tighten minimum astropy/numpy/scipy dependency versions

[steven-murray]

Summary

• The underlying crash reported in [Feature Req] More detailed dependency list #286 ('FlatLambdaCDM' object has no attribute '_nu_info') was already fixed on main by fix: replace deprecated _nu_info with public has_massive_nu API #307, which replaced the private cosmo._nu_info.has_massive_nu access with the public cosmo.has_massive_nu/cosmo.nu_relative_density API.
• The remaining ask in [Feature Req] More detailed dependency list #286 — a more accurate dependency floor — was not addressed. pyproject.toml still listed numpy>=1.6.2, scipy>=0.12.0, astropy>=1.1, versions that predate this project's requires-python = ">=3.12" by years. Because pip only upgrades a package when the installed version doesn't satisfy the constraint, an environment with an old-but-installed astropy could silently keep it ("Requirement already satisfied") instead of picking a version that actually matches what hmf needs.
• Bumped the floors to the earliest release of each package that supports Python 3.12: numpy>=1.26, scipy>=1.11, astropy>=6.0. Regenerated uv.lock to match.

Test plan

• uv run pytest tests/test_growth.py tests/test_transfer.py tests/test_cosmo.py — 64 passed, 1 skipped
• uv lock regenerates cleanly with no other changes

Fixes #286

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.86%. Comparing base (0cc28ed) to head (6cff360).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #316   +/-   ##
=======================================
  Coverage   97.86%   97.86%           
=======================================
  Files          26       26           
  Lines        2671     2671           
=======================================
  Hits         2614     2614           
  Misses         57       57           

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