Migrate Python tests off the deprecated 0.7 call forms #214

Problem

0.8 introduced train / set_centroids / add, and the 0.7 forms (positional constructor
options, build, positional add options and others listed in #213) now raise
DeprecationWarning. 0.9 removes them. Many Python tests still use the 0.7 forms only for setup, so they
emit warnings now and will break in 0.9.

Task

Rewrite test setup that uses a deprecated form only to create or fill an index, using the
0.8 API.
This is a tracking issue: one PR per file (or a few small files) is ideal. The maintainers
are migrating the remaining files.

# 0.7 form
index.build(data, centroids, cluster_ids, num_threads=1)
# 0.8 form
index.set_centroids(centroids)
index.add(data, cluster_ids=cluster_ids, num_threads=1)

The migration guide lists
every mapping, including HNSW and SymphonyQG.

Rules

• Keep each test's intent. A test of 0.7-only behavior with no 0.8 form (such as build
  replacing an index, or validation of max_elements and quantization_bits) moves to
  test_compat_08.py, which Remove the deprecated 0.7 Python call forms #213 deletes; wrap its deprecated calls in that file's quietly
  or single_deprecation. If test_compat_08.py already covers it, delete it instead. Say
  which in the PR. Known cases: test_hnsw.py::test_rejected_rebuild_preserves_index and
  test_zero_capacity_raises, test_symqg.py::test_failed_rebuild_preserves_index,
  test_successful_rebuild_replaces_index and test_invalid_quantization_bits_raises, and
  test_input_boundaries.py::test_build_row_count_diagnostics.
• Do not change the existing tests in these files: test_compat_08.py, test_txtai_compat.py,
  test_train_api.py, test_symqg_api.py (they test compatibility or equivalence on purpose).
• HNSW defaults differ: the 0.7 constructor used nbits=8 and the 0.8 one uses nbits=7, so
  pass nbits= explicitly. set_centroids needs HnswIndex(..., num_clusters=len(centroids)),
  while the 0.7 build accepted any number of centroids.
• max_elements no longer comes from the constructor: a new IvfIndex starts at 0 and grows
  to the stored count, and HnswIndex grows on add. Update expected max_elements values
  and reprs; where a test needs a preallocated capacity, use HnswIndex.resize(n) (see test(python): migrate index count tests to the 0.8 API #226).
• Pass num_threads explicitly where the old call relied on its default: build defaulted
  to 1 thread, while add defaults to all CPUs. Tests that compare bytes or exact results
  need the same thread count as before.
• Run the edited file with python -m pytest -W error::DeprecationWarning tests/python/<file>
  to confirm no deprecated call remains; this also catches deprecated constructor forms
  and properties that a search for .build( misses.

Files

Files with tests that fail under -W error::DeprecationWarning at v0.8.2, excluding the four
above.

• test_ivf.py
• test_hnsw.py
• test_symqg.py
• test_input_boundaries.py
• test_ivf_initializers.py
• test_portable_indexes.py, test_import.py
• test_index_counts.py (test(python): migrate index count tests to the 0.8 API #226)
• test_build_cluster_ids.py, test_large_dimensions.py, test_array_alignment.py,
  test_concurrent_indexes.py, test_thread_counts.py, test_persistence_paths.py,
  test_index_repr.py, test_kmeans_sampling.py, test_remove_arrays.py,
  test_quantization_factors.py (test(python): migrate ten test files off the 0.7 call forms #227)

The seven unchecked files are also changed by #222. #227 also applied the #216 fixes to the
graph cases of test_array_alignment.py and test_thread_counts.py.

Setup and checks: contribution guide, Python changes.