Format faiss Python files with black (line length 80)

[limqiying]

Summary:

this is a no-op change

Ran black -l 80 over all tracked Python files under fbcode/faiss/, using line length 80 to match faiss's documented coding style (CONTRIBUTING.md: "80 character line length (both for C++ and Python)"). 172 files were reformatted; 28 were already compliant.

This is a pure-formatting change. black runs its AST-equivalence safety check on every file, so no identifiers, string/numeric values, operators, or control flow were altered — only whitespace, indentation, line wrapping, blank lines, trailing commas, and string-quote normalization (single to double quotes).

fbcode/faiss/ is intentionally excluded from Meta's standard Python autoformatter (arc f / arc lint -a report no formatter for these paths) because it mirrors to public GitHub, so the Python had drifted out of any consistent style. The C++ is already clang-format-clean (0 of 807 files change), so this effort is Python-only. This diff brings the Python to canonical black formatting.

Excluded demos/index_pq_flat_separate_codes_from_codebook.py: it contains a Jupyter !rm shell-magic line and is not valid Python, so black cannot parse it.

This is the base of a 3-diff stack: (1) this black reformat; (2) .flake8 alignment (max-line-length 80 + black-compatible ignores E203/W503); (3) genuine lint fixes (F401/F403/F841/B011).

Differential Revision: D109736099

[meta-codesync]

@limqiying has exported this pull request. If you are a Meta employee, you can view the originating Diff in D109736099.