[ENH] Layout Query Plan and Executor interface in frontend (#2920)

## Description of changes

*Summarize the changes made by this PR.*
 - Improvements & Bug fixes
	 - N/A
 - New functionality
	 - Defines the query operators and query plan, which is the first step towards query pushdown for distributed Chroma.
	 - Defines the executor abstract class, which should execute any variant of query plan. Also provides dummy implementation for both local and distributed chroma.

## Test plan
*How are these changes tested?*

- [x] Tests pass locally with `pytest` for python, `yarn test` for js, `cargo test` for rust

## Documentation Changes
*Are all docstrings for user-facing APIs updated if required? Do we need to make documentation changes in the [docs repository](https://github.com/chroma-core/docs)?*
N/A

chromadb/execution/executor/abstract.py

@@ -0,0 +1,19 @@
+from abc import abstractmethod
+from typing import Sequence
+from chromadb.config import Component
+from chromadb.execution.expression.plan import CountPlan, GetPlan, KNNPlan
+from chromadb.types import MetadataEmbeddingRecord, VectorEmbeddingRecord
+
+
+class Executor(Component):
+    @abstractmethod
+    def count(self, plan: CountPlan) -> int:
+        pass
+
+    @abstractmethod
+    def get(self, plan: GetPlan) -> Sequence[MetadataEmbeddingRecord]:
+        pass
+
+    @abstractmethod
+    def knn(self, plan: KNNPlan) -> Sequence[Sequence[VectorEmbeddingRecord]]:
+        pass

chromadb/execution/executor/distributed.py

@@ -0,0 +1,27 @@
+from typing import Sequence
+from overrides import overrides
+from chromadb.config import System
+from chromadb.execution.executor.abstract import Executor
+from chromadb.execution.expression.plan import CountPlan, GetPlan, KNNPlan
+from chromadb.segment import SegmentManager
+from chromadb.types import MetadataEmbeddingRecord, VectorEmbeddingRecord
+
+
+class DistributedExecutor(Executor):
+    _manager: SegmentManager
+
+    def __init__(self, system: System):
+        super().__init__(system)
+        self._manager = self.require(SegmentManager)
+
+    @overrides
+    def count(self, plan: CountPlan) -> int:
+        return 0
+
+    @overrides
+    def get(self, plan: GetPlan) -> Sequence[MetadataEmbeddingRecord]:
+        return list()
+
+    @overrides
+    def knn(self, plan: KNNPlan) -> Sequence[Sequence[VectorEmbeddingRecord]]:
+        return list()

chromadb/execution/executor/local.py

@@ -0,0 +1,27 @@
+from typing import Sequence
+from overrides import overrides
+from chromadb.config import System
+from chromadb.execution.executor.abstract import Executor
+from chromadb.execution.expression.plan import CountPlan, GetPlan, KNNPlan
+from chromadb.segment import SegmentManager
+from chromadb.types import MetadataEmbeddingRecord, VectorEmbeddingRecord
+
+
+class LocalExecutor(Executor):
+    _manager: SegmentManager
+
+    def __init__(self, system: System):
+        super().__init__(system)
+        self._manager = self.require(SegmentManager)
+
+    @overrides
+    def count(self, plan: CountPlan) -> int:
+        return 0
+
+    @overrides
+    def get(self, plan: GetPlan) -> Sequence[MetadataEmbeddingRecord]:
+        return list()
+
+    @overrides
+    def knn(self, plan: KNNPlan) -> Sequence[Sequence[VectorEmbeddingRecord]]:
+        return list()

chromadb/execution/expression/operator.py

@@ -0,0 +1,45 @@
+from dataclasses import dataclass
+from typing import Optional
+
+from chromadb.api.types import Embeddings, IDs
+from chromadb.types import RequestVersionContext, Where, WhereDocument, Collection
+
+
+@dataclass
+class Scan:
+    collection: Collection
+
+    @property
+    def version(self) -> RequestVersionContext:
+        return RequestVersionContext(
+            collection_version=self.collection.version,
+            log_position=self.collection.log_position,
+        )
+
+
+@dataclass
+class Filter:
+    user_ids: Optional[IDs] = None
+    where: Optional[Where] = None
+    where_document: Optional[WhereDocument] = None
+
+
+@dataclass
+class KNN:
+    embeddings: Embeddings
+    fetch: int
+
+
+@dataclass
+class Limit:
+    skip: int = 0
+    fetch: Optional[int] = None
+
+
+@dataclass
+class Projection:
+    document: bool = False
+    embedding: bool = False
+    metadata: bool = False
+    rank: bool = False
+    uri: bool = False

chromadb/execution/expression/plan.py

@@ -0,0 +1,24 @@
+from dataclasses import dataclass, field
+
+from chromadb.execution.expression.operator import KNN, Filter, Limit, Projection, Scan
+
+
+@dataclass
+class CountPlan:
+    scan: Scan
+
+
+@dataclass
+class GetPlan:
+    scan: Scan
+    filter: Filter = field(default_factory=Filter)
+    limit: Limit = field(default_factory=Limit)
+    projection: Projection = field(default_factory=Projection)
+
+
+@dataclass
+class KNNPlan:
+    scan: Scan
+    knn: KNN
+    filter: Filter = field(default_factory=Filter)
+    projection: Projection = field(default_factory=Projection)