Fix #766: handle missing terms-of-use columns gracefully

[bleedblack1]

Summary

Fixes #766

When terms_of_use_expiry_date or terms_of_use_url columns are missing
from the manifest (e.g. during pre-release), functions like
lookup_terms_of_use_info() and _sample_set_has_unrestricted_use()
previously raised a cryptic KeyError. They now raise a clear,
descriptive ValueError with a helpful message.

Changes

• malariagen_data/anoph/base.py:

  • lookup_terms_of_use_info(): gracefully handles missing
    terms-of-use columns, raises descriptive ValueError
  • _sample_set_has_unrestricted_use(): raises descriptive
    ValueError when unrestricted_use column is missing
  • Fixed cache logic indentation bug in lookup_terms_of_use_info()

• tests/anoph/test_base.py:

  • test_lookup_terms_of_use_info_missing_columns: verifies correct
    error when columns are missing
  • test_sample_set_has_unrestricted_use_missing_column: verifies
    correct error for missing unrestricted_use column
  • test_sample_sets_no_terms_of_use: verifies sample_sets()
    still works when terms-of-use columns are absent

Test Results

• 34/34 tests passing locally (Python 3.11)
• Coverage passing
• Linting passing

[bleedblack1]

All 34 tests pass locally on Python 3.11, including on the master branch.
The tests (3.12, >=2.0.2,<2.1) CI failure appears to be a pre-existing
infrastructure issue unrelated to this PR.

• Coverage passing
• Linting passing
• 34/34 tests passing locally

Ready for review! @jonbrenas @tristanpwdennis