Replace the Python-defined OptimizerRule/AnalyzerRule approach with FFI-imported physical optimizer rules.

The Python logical-rule approach could observe plans but not transform them: there are no Python constructors for LogicalPlan node variants, so a rule could only return None or the input plan unchanged. The audience for custom rules also overlaps strongly with people who can write Rust.

DataFusion exposes no FFI bridge for the logical OptimizerRule/AnalyzerRule traits, but it does export FFI_PhysicalOptimizerRule for the physical PhysicalOptimizerRule trait. This commit imports those instead.

Changes:

* Remove crates/core/src/optimizer_rules.rs, python/datafusion/optimizer.py, python/tests/test_optimizer.py, and the SessionContext.add_optimizer_rule / add_analyzer_rule methods. remove_optimizer_rule is unchanged (pre-existing).
* New crates/core/src/physical_optimizer.rs reads a __datafusion_physical_optimizer_rule__ capsule and converts it via Arc<dyn PhysicalOptimizerRule>::from(&FFI_PhysicalOptimizerRule).
* SessionContext gains a physical_optimizer_rules constructor argument. Upstream offers no API to add physical rules to a live context, so they are appended to the builder at construction time only.
* The datafusion-ffi-example crate gains MyPhysicalOptimizerRule, a counter-backed rule used by _test_physical_optimizer_rule.py to prove the rule fires over FFI during physical planning.

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

Replace the `list[Any]` hint on the SessionContext `physical_optimizer_rules` argument with a `PhysicalOptimizerRuleExportable` Protocol, matching the existing `TableProviderExportable` / `*Exportable` pattern used for other FFI-capsule objects.

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

The PyCapsule / FFI_PhysicalOptimizerRule mechanics describe the Protocol, not the SessionContext constructor. Move that detail onto PhysicalOptimizerRuleExportable and leave the constructor argument docs focused on behavior.

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

Remove the explanatory comment about FFI bridge availability; the same information already lives on PhysicalOptimizerRuleExportable.

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

Sibling FFI-import modules (udf, udaf, catalog, table) carry no module-level docs, and the rst-style markup did not match Rust conventions. The function doc comment already states intent.

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

Replace the hand-written crates/core/src/physical_optimizer.rs with a `from_pycapsule!` invocation in the util crate, matching `physical_codec_from_pycapsule` and the other FFI capsule importers. The macro already handles the hasattr/getattr/cast/validate/pointer_checked sequence and the infallible `Arc::from(&FFI)` conversion, so the dedicated module is no longer needed.

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

Drop the sentence about logical-rule FFI availability; it is background, not type-hint information, and keeps the Protocol docstring in line with the other *Exportable hints.

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

Coverage subsumed by test_ffi_physical_optimizer_rule_runs_during_planning,
which exercises the same capsule export via add_physical_optimizer_rule.

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