estuary-cdk: prevent state mutations by deep copying initial_state`

Previously when initializing the state of a binding, the CDK was
directly referencing the `initial_state` of the binding and any
modifications made to the binding's `state` would also be reflected in
the `initial_state`. While this works when all bindings have their own
distinct `initial_state`s, this would cause unintended mutations if the
same `initial_state` was used for multiple bindings.

Instead, the CDK now creates a deep copy of the `initial_state` when
initializing a binding's `state`. This prevents mutations to `state`
from affecting `initial_state`.

Author: Alex-Bair

estuary-cdk/estuary_cdk/capture/common.py

@@ -573,14 +573,14 @@ async def _run(task: Task):
                     ):
                         initialized_backfill_state = resource.initial_state.backfill
                         initialized_backfill_state.cutoff = state.inc.cursor
-                        state.backfill = initialized_backfill_state
+                        state.backfill = initialized_backfill_state.model_copy(deep=True)
                     # In all other cases, wipe the state back to the initial state.
                     else:
-                        state = resource.initial_state
+                        state = resource.initial_state.model_copy(deep=True)
 
                     state.is_connector_initiated = True
                 else:
-                    state = resource.initial_state
+                    state = resource.initial_state.model_copy(deep=True)
 
                 state.last_initialized = NOW