feat: add python functools reduce

[kvz]

Summary

• add python/functools/reduce with Python-style omitted-initializer semantics
• add focused util/generated coverage and parity support for simple reducer callbacks
• remove the stale functools/reduce wishlist entry and refresh website/upstream-surface data

Validation

• corepack yarn exec vitest run test/util/python-functools-harvest-1.vitest.ts
• corepack yarn test:parity python/functools/reduce --no-cache
• corepack yarn exec vitest run test/generated/python/functools/*.vitest.ts
• corepack yarn test:upstream-surface python
• corepack yarn website:verify
• corepack yarn check
• ~/code/dotfiles/bin/council.ts review (one real finding fixed; one reviewer failed for capacity)