fix!: remove chunk_id property from Chunk class (#3954)

# What does this PR do?

chunk_id in the Chunk class executes actual logic to compute a chunk ID.
This sort of logic should not live in the API spec.

Instead, the providers should be in charge of calling generate_chunk_id,
and pass it to `Chunk`.

this removes the incorrect dependency between Provider impl and API impl

Signed-off-by: Charlie Doern <cdoern@redhat.com>

tests/unit/providers/vector_io/conftest.py

@@ -43,9 +43,15 @@ def embedding_dimension() -> int:
 @pytest.fixture(scope="session")
 def sample_chunks():
     """Generates chunks that force multiple batches for a single document to expose ID conflicts."""
+    from llama_stack.providers.utils.vector_io.vector_utils import generate_chunk_id
+
     n, k = 10, 3
     sample = [
-        Chunk(content=f"Sentence {i} from document {j}", metadata={"document_id": f"document-{j}"})
+        Chunk(
+            content=f"Sentence {i} from document {j}",
+            chunk_id=generate_chunk_id(f"document-{j}", f"Sentence {i} from document {j}"),
+            metadata={"document_id": f"document-{j}"},
+        )
         for j in range(k)
         for i in range(n)
     ]
@@ -53,6 +59,7 @@ def sample_chunks():
         [
             Chunk(
                 content=f"Sentence {i} from document {j + k}",
+                chunk_id=f"document-{j}-chunk-{i}",
                 chunk_metadata=ChunkMetadata(
                     document_id=f"document-{j + k}",
                     chunk_id=f"document-{j}-chunk-{i}",
@@ -73,6 +80,7 @@ def sample_chunks_with_metadata():
     sample = [
         Chunk(
             content=f"Sentence {i} from document {j}",
+            chunk_id=f"document-{j}-chunk-{i}",
             metadata={"document_id": f"document-{j}"},
             chunk_metadata=ChunkMetadata(
                 document_id=f"document-{j}",