Prepare v4.0.0 release

[lukekim]

Summary

Prepares the v4.0.0 release: updates docs to match the implementation, bumps the version, consolidates packaging into pyproject.toml, and switches Spice.ai Cloud endpoints to the region-specific hostnames.

Changes

Version & packaging

• Bump version to 4.0.0 (now defined statically in pyproject.toml; dynamic = ["version"] removed).
• Consolidate packaging into pyproject.toml. Removed:
  • setup.py
  • requirements.txt
  • test.requirements.txt
  • MANIFEST.in
• Update .github/workflows/version.yml and .github/CODEOWNERS and the release-checklist issue template to point at pyproject.toml instead of setup.py.
• Verified: python -m build produces a clean sdist and wheel.

Region-specific Cloud endpoints

The legacy flight.spiceai.io / data.spiceai.io hostnames are no longer valid. Updated to region-specific defaults:

• grpc+tls://us-east-1-prod-aws-flight.spiceai.io
• https://us-east-1-prod-aws-data.spiceai.io

Also fixed Client(http_url=...) to default to the local URL (previously defaulted to the cloud URL while flight_url defaulted to local).

Docs

• Rewrote README.md to cover everything the implementation now ships:
  • Typed query helpers (query_arrow/pandas/polars/pylist/pydict/batches)
  • DataFrame API (client.table/sql/from_arrow/from_pandas/from_pydict)
  • Expr DSL (col, lit, case) and spicepy.functions
  • Catalog introspection (catalogs, schemas, tables, describe, get_schema, explain, show)
  • Writers (write_parquet, write_csv, write_json)
  • Parameterized queries via params= and query_with_params
• Install instructions use pip install git+https://github.com/spiceai/spicepy@v4.0.0 (spicepy is not on PyPI under that name).
• Bumped documented Python requirement to 3.11+ (matches pyproject.toml).
• Added docs/release_notes/v4.0.0.md.

Breaking changes (documented in release notes)

• Region-specific Cloud endpoints required.
• Client(http_url=...) now defaults to local.
• Python ≥ 3.11.
• Core dep major bumps (pyarrow 24, pandas 3, certifi 2026.4.22, requests 2.34).
• Empty api_key strings treated as None (already in trunk via Handle empty api_key #133).