Add produce() function for proxy-based patch generation (issue #8)

Introduce `produce()` as a new public API that uses proxy objects (DictProxy, ListProxy, SetProxy) to track mutations in real-time and emit JSON patches as changes occur — an alternative to post-hoc diff().

- Add patchdiff/produce.py with proxy classes and PatchRecorder
- Support optional observ reactive objects via to_raw() integration
- Add in_place option to mutate the original object directly
- Fix Pointer.__eq__ type hint and modernize tuple return type hint
- Expand benchmarks with produce() vs diff() and observ comparisons
- Add comprehensive tests for dict, list, set, core, and observ integration
- Update README with produce() usage examples

Author: berendkleinhaneveld

.github/workflows/benchmark.yml

@@ -21,7 +21,7 @@ jobs:
           python-version: "3.14"
 
       - name: Install dependencies
-        run: uv sync
+        run: uv sync --group observ
 
       # On PRs: run benchmarks twice (PR code vs master code) and compare
       - name: Run benchmarks

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
         with:
           python-version: ${{ matrix.pyversion }}
       - name: Install dependencies
-        run: uv sync
+        run: uv sync --group observ
       - name: Lint
         run: uv run ruff check
       - name: Format
@@ -61,7 +61,7 @@ jobs:
         with:
           python-version: "3.9"
       - name: Install dependencies
-        run: uv sync
+        run: uv sync --group observ
       - name: Build wheel
         run: uv build
       - name: Twine check

README.md

@@ -43,3 +43,54 @@ print(to_json(ops, indent=4))
 #     }
 # ]
 ```
+
+## Proxy-based patch generation
+
+For better performance, `produce()` can be used which generates patches by tracking mutations on a proxy object (inspired by [Immer](https://immerjs.github.io/immer/produce)):
+
+```python
+from patchdiff import produce
+
+base = {"count": 0, "items": [1, 2, 3]}
+
+def recipe(draft):
+    """Mutate the draft object - changes are tracked automatically."""
+    draft["count"] = 5
+    draft["items"].append(4)
+    draft["new_field"] = "hello"
+
+result, patches, reverse_patches = produce(base, recipe)
+
+# base is unchanged (immutable by default)
+assert base == {"count": 0, "items": [1, 2, 3]}
+
+# result contains the changes
+assert result == {"count": 5, "items": [1, 2, 3, 4], "new_field": "hello"}
+
+# patches describe what changed
+print(patches)
+# [
+#     {"op": "replace", "path": "/count", "value": 5},
+#     {"op": "add", "path": "/items/-", "value": 4},
+#     {"op": "add", "path": "/new_field", "value": "hello"}
+# ]
+```
+
+When immutability is not needed, it is possible to apply the ops directly, improving performance even further by not having to make a `deepcopy` of the given state. 
+
+```python
+from observ import reactive
+from patchdiff import produce
+
+state = reactive({"count": 0})
+
+# Mutate in place and get patches for undo/redo
+result, patches, reverse = produce(
+    state, 
+    lambda draft: draft.update({"count": 5}), 
+    in_place=True,
+)
+
+assert result is state  # Same object
+assert state["count"] == 5  # State was mutated, watchers triggered
+```