add proto converter reference to PhysicalExtensionCodec

[jayshrivastava]

Which issue does this PR close?

• Closes add PhysicalProtoConverterExtension to PhysicalExtensionCodec #21056

Rationale for this change

Custom ExecutionPlan nodes that store PhysicalExpr fields cannot participate in expression deduplication during serialization because PhysicalExtensionCodec::try_encode/try_decode lack access to the PhysicalProtoConverterExtension.

What changes are included in this PR?

• Added proto_converter: &dyn PhysicalProtoConverterExtension parameter
  to PhysicalExtensionCodec::try_decode and try_encode
• Updated all implementations: DefaultPhysicalExtensionCodec,
  ComposedPhysicalExtensionCodec, ForeignPhysicalExtensionCodec (FFI),
  and all examples
• Updated call sites in PhysicalPlanNode serialization/deserialization
• FFI bridge passes DefaultPhysicalProtoConverter as a fallback

Are these changes tested?

Yes — added test_custom_node_with_dynamic_filter_dedup_roundtrip which
verifies that a DynamicFilterPhysicalExpr shared between a FilterExec
and a custom ExecutionPlan node preserves its shared inner state after a
roundtrip through DeduplicatingProtoConverter.

Are there any user-facing changes?

Breaking API change: PhysicalExtensionCodec::try_decode and try_encode
now take an additional &dyn PhysicalProtoConverterExtension parameter.
All custom codec implementations must be updated.