feat: make SSZVector of Fp serializable (#223)

* feat: make Fp and its vector json serializable

* fix: remove unneeded Fp.__get_pydantic_core_schema()

* fix: remove no longer needed imports

* fix: align naming

* test: Fp list and vector

* fix: linting

Author: unnawut

src/lean_spec/types/collections.py

@@ -45,6 +45,25 @@ class Uint16Vector2(SSZVector):
     data: Tuple[SSZType, ...] = Field(default_factory=tuple)
     """The immutable data stored in the vector."""
 
+    @field_serializer("data", when_used="json")
+    def _serialize_data(self, value: Tuple[SSZType, ...]) -> list[Any]:
+        """Serialize vector elements to JSON, preserving custom type serialization."""
+        from lean_spec.subspecs.koalabear import Fp
+
+        result: list[Any] = []
+        for item in value:
+            # For BaseBytes subclasses, manually add 0x prefix
+            if isinstance(item, BaseBytes):
+                result.append("0x" + item.hex())
+            # For Fp field elements, extract the value attribute
+            elif isinstance(item, Fp):
+                result.append(item.value)
+            else:
+                # For other types (Uint, etc.), convert to int
+                # BaseUint inherits from int, so this cast is safe
+                result.append(item)
+        return result
+
     @field_validator("data", mode="before")
     @classmethod
     def _validate_vector_data(cls, v: Any) -> Tuple[SSZType, ...]:
@@ -188,11 +207,16 @@ class Uint64List32(SSZList):
     @field_serializer("data", when_used="json")
     def _serialize_data(self, value: Tuple[SSZType, ...]) -> list[Any]:
         """Serialize list elements to JSON, preserving custom type serialization."""
+        from lean_spec.subspecs.koalabear import Fp
+
         result: list[Any] = []
         for item in value:
             # For BaseBytes subclasses, manually add 0x prefix
             if isinstance(item, BaseBytes):
                 result.append("0x" + item.hex())
+            # For Fp field elements, extract the value attribute
+            elif isinstance(item, Fp):
+                result.append(item.value)
             else:
                 # For other types (Uint, etc.), convert to int
                 # BaseUint inherits from int, so this cast is safe

tests/lean_spec/types/test_collections.py

@@ -6,6 +6,7 @@
 from pydantic import ValidationError, create_model
 from typing_extensions import Type
 
+from lean_spec.subspecs.koalabear import Fp
 from lean_spec.types.boolean import Boolean
 from lean_spec.types.collections import SSZList, SSZVector
 from lean_spec.types.container import Container
@@ -149,6 +150,13 @@ class Uint8Vector2(SSZVector):
     LENGTH = 2
 
 
+class FpVector8(SSZVector):
+    """A vector of exactly 8 Fp values."""
+
+    ELEMENT_TYPE = Fp
+    LENGTH = 8
+
+
 # Additional List classes for tests
 class Uint8List32(SSZList):
     """A list with up to 32 Uint8 values."""
@@ -178,6 +186,13 @@ class BooleanList4(SSZList):
     LIMIT = 4
 
 
+class FpList8(SSZList):
+    """A list with up to 8 Fp values."""
+
+    ELEMENT_TYPE = Fp
+    LIMIT = 8
+
+
 # Test data for the 'sig' vector test case
 sig_test_data_list = [0] * 96
 for i, v in {0: 1, 32: 2, 64: 3, 95: 0xFF}.items():
@@ -335,6 +350,11 @@ class TestSSZVectorSerialization:
                 (FixedContainer(a=Uint8(1), b=Uint16(2)), FixedContainer(a=Uint8(3), b=Uint16(4))),
                 "010200030400",  # 010200 for first element, 030400 for second
             ),
+            (
+                FpVector8,
+                (10, 20, 30, 40, 50, 60, 70, 80),
+                "0a000000140000001e00000028000000320000003c0000004600000050000000",
+            ),
         ],
     )
     def test_fixed_size_element_vector_serialization(
@@ -372,7 +392,7 @@ def test_variable_size_element_vector_serialization(self) -> None:
         assert decoded == instance
 
 
-class TestListSerialization:
+class TestSSZListSerialization:
     """Tests SSZ serialization and deserialization for the List type."""
 
     @pytest.mark.parametrize(
@@ -397,6 +417,11 @@ class TestListSerialization:
                 tuple(range(1, 20)),
                 "".join(i.to_bytes(32, "little").hex() for i in range(1, 20)),
             ),
+            (
+                FpList8,
+                (10, 20, 30),
+                "0a000000140000001e000000",
+            ),
         ],
     )
     def test_fixed_size_element_list_serialization(