Make`LiteralPredicate` predicate JSON serializable

[Fokko]

Feature Request / Improvement

Make sure that the LiteralPredicate can be serialized to JSON:

iceberg-python/pyiceberg/expressions/__init__.py

Line 722 in e5e7453

class LiteralPredicate(UnboundPredicate[L], ABC):

This predicate has four implementations: IsNull, NotNull, IsNaN, and NotNan, and translates to:

{
    "type": "lt" // Or lt-eq, gt, gt-eq, eq, not-eq, starts-with, not-starts-with
    "term": str, // The column name
    "value": Any // Should be Literal, but we can do that later since that's not JSON serializable yet
}

We use Pydantic for JSON serialization, which can be enabled by deriving from the IcebergBaseModel:

iceberg-python/pyiceberg/partitioning.py

Line 124 in e5e7453

class PartitionSpec(IcebergBaseModel):

Example tests can be found here:

iceberg-python/tests/table/test_partitioning.py

Lines 116 to 132 in e5e7453

	def test_serialize_partition_spec() -> None:
	partitioned = PartitionSpec(
	PartitionField(source_id=1, field_id=1000, transform=TruncateTransform(width=19), name="str_truncate"),
	PartitionField(source_id=2, field_id=1001, transform=BucketTransform(num_buckets=25), name="int_bucket"),
	spec_id=3,
	)
	assert (
	partitioned.model_dump_json()
	== """{"spec-id":3,"fields":[{"source-id":1,"field-id":1000,"transform":"truncate[19]","name":"str_truncate"},{"source-id":2,"field-id":1001,"transform":"bucket[25]","name":"int_bucket"}]}"""
	)
	def test_deserialize_unpartition_spec() -> None:
	json_partition_spec = """{"spec-id":0,"fields":[]}"""
	spec = PartitionSpec.model_validate_json(json_partition_spec)
	assert spec == PartitionSpec(spec_id=0)

[tanmayrauth]

Hi @Fokko, can work on this issue?

[axwell0]

May I take on this issue?