feat: inline encoding for Python aggregate and window UDFs

Extends the PythonLogicalCodec / PythonPhysicalCodec inline encoding
introduced for scalar UDFs to also cover Python-defined aggregate and
window UDFs. The cloudpickle tuple shape per family is:

  DFPYUDA  (agg)     (name, accumulator_factory, input_schema_bytes,
                      return_schema_bytes, state_schema_bytes,
                      volatility_str)
  DFPYUDW  (window)  (name, evaluator_factory, input_schema_bytes,
                      return_schema_bytes, volatility_str)

Same wire-framing as scalar (family magic + version byte + cloudpickle
blob), same schema serde (arrow-rs native IPC), same cached cloudpickle
handle. The agg state schema is encoded as a full IPC schema so the
post-decode UDF reports the same names + nullability + metadata as the
sender — relevant for accumulators whose StateFieldsArgs consumers key
off names rather than positional DataType.

Required restructuring two existing UDF impls so the codec can grab
the Python callable directly:

* udaf.rs: replaces create_udaf + AccumulatorFactoryFunction closure
  with a named PythonFunctionAggregateUDF that stores the Py<PyAny>
  accumulator factory. Synthesizes state_{i} field names when the
  Python constructor passes only Vec<DataType>; from_parts preserves
  the full state schema on the decode side.
* udwf.rs: renames MultiColumnWindowUDF -> PythonFunctionWindowUDF,
  drops the PartitionEvaluatorFactory PtrEq wrapper, stores the
  Py<PyAny> evaluator directly. PartialEq and Hash get the same
  pointer-identity fast path + debug-log exception handling already
  on PythonFunctionScalarUDF.

User-facing surface:

* AggregateUDF.name and WindowUDF.name properties (parallel to the
  ScalarUDF.name shipped in PR1).
* Existing UDAF/UDWF construction paths are unchanged.

The per-session with_python_udf_inlining toggle, sender-side context,
strict refusal, and user-guide docs land in PRs 3-4 of this series.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer