[BREAKING] Python: Checkpoint refactor: encode/decode, checkpoint format, etc (#3744)

* WIP: Checkpoint refactor: encode/decode, checkpoint format, etc

* WIP: Remove workflow ID in checkpoints

* Refactor checkpointing

* Add get_latest tests

* Increase test coverage

* Fix formatting

* Fix unit tests

* Fix samples

* fix unit tests

* fix pipeline

* Copilot comments

* Fix tests

* Fix more tests

* Address comments part 1

* Address comments part 2

* Comments

python/.cspell.json

@@ -24,8 +24,8 @@
     ],
     "words": [
         "aeiou",
-        "aiplatform",
         "agui",
+        "aiplatform",
         "azuredocindex",
         "azuredocs",
         "azurefunctions",
@@ -57,20 +57,22 @@
         "nopep",
         "NOSQL",
         "ollama",
-        "otlp",
         "Onnx",
         "onyourdatatest",
         "OPENAI",
         "opentelemetry",
         "OTEL",
+        "otlp",
         "powerfx",
         "protos",
         "pydantic",
         "pytestmark",
         "qdrant",
         "retrywrites",
-        "streamable",
         "serde",
+        "streamable",
+        "superstep",
+        "supersteps",
         "templating",
         "uninstrument",
         "vectordb",