v0.48.0

Publishes the Python SDK for the successor VGI wire contract, vgi.v3 / 3.0.0.

• Canonical catalog metadata now covers nested schema paths, nullable default schemas, column expressions/comments/tags, macro overload families, typed constraints and indexes, dependencies, and view/security metadata.
• Adds typed prepared-query contracts, explicit statements through existing query calls, structured scalar projection negotiation, and bind-scoped scan repeatability.
• Requires published vgi-rpc>=0.52.3 for complete outer IPC framing. Includes the one-shot writable-scan continuation fix.
• Keeps the existing Arrow C++ generator as the default and adds an explicit Nanoarrow backend for the DuckDB 2.0 adapter. Nested Go schema output now reproduces gofmt without changing wire shapes or hashes.
• Completes strict typing for the new protocol tests and reference providers, preserving malformed-input and absent-object tests.

Compatibility: requires a native VGI build that speaks vgi.v3 / 3.0.0; older vgi.v2 extensions are incompatible. The protocol is qualified with the DuckDB 1.5 adapter and the DuckDB 2.0/Nanoarrow candidate. Automatic whole-query pushdown remains separate adapter work.

Validation: Ruff, strict mypy for runtime and tests, package builds and metadata checks passed. The full Python suite qualified 4,609 passing tests with 192 expected/environment skips; four initial failures were resolved by one stub-only cast correction and an exact Rust checkout path, then targeted tests passed. Existing full native SDK language matrices and canonical HTTP qualification cover the runtime changes.

The core wheel continues to bundle import-only fixture modules. The separate vgi-fixtures wheel is built and checked, while its PyPI publication remains disabled because that project has not been provisioned.