feat: support for loop

[aglinxinyuan]

Main changes for the Basic For Loop:

1. Loop Operator:

• LoopStart Operator
• LoopEnd Operator

2. ECM:

• IterationEnd

3. DCM:

• NextIteration

Life Cycle of Basic For Loop:

[Copilot]

Pull Request Overview

This PR adds support for basic for-loop semantics by introducing LoopStart and LoopEnd operators, new iteration control messages, and the necessary execution and RPC plumbing in both Scala and Python runtimes.

• Introduced LoopStart/LoopEnd executors and descriptors to buffer and replay tuples across iterations
• Defined EndIteration and NextIteration control messages and integrated them into DataProcessor, OutputManager, and RPC handlers
• Updated Python runner, protobuf definitions, and internal models to handle iteration lifecycle

Reviewed Changes

Copilot reviewed 25 out of 28 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/sleep/SleepOpExec.scala	Added Sleep operator executor
core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/sleep/SleepOpDesc.scala	Defined Sleep operator descriptor
core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/loop/LoopStartOpExec.scala	Implemented LoopStart executor
core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/loop/LoopStartOpDesc.scala	Defined LoopStart descriptor
core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/loop/LoopEndOpExec.scala	Implemented LoopEnd executor
core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/loop/LoopEndOpDesc.scala	Defined LoopEnd descriptor
core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/LogicalOp.scala	Imported new loop and sleep operators
core/workflow-core/src/main/scala/edu/uci/ics/amber/core/tuple/TupleLike.scala	Added FinalizeIteration marker
core/workflow-core/src/main/scala/edu/uci/ics/amber/core/executor/OperatorExecutor.scala	Added reset lifecycle method
core/amber/src/main/scala/edu/uci/ics/amber/engine/architecture/worker/promisehandlers/StartChannelHandler.scala	Refactored start-channel handling
core/amber/src/main/scala/edu/uci/ics/amber/engine/architecture/worker/promisehandlers/NextIterationHandler.scala	Added NextIteration RPC handler
core/amber/src/main/scala/edu/uci/ics/amber/engine/architecture/worker/promisehandlers/EndIterationHandler.scala	Added EndIteration RPC handler
core/amber/src/main/scala/edu/uci/ics/amber/engine/architecture/worker/promisehandlers/EndChannelHandler.scala	Updated end-channel to finalize loops
core/amber/src/main/scala/edu/uci/ics/amber/engine/architecture/worker/DataProcessorRPCHandlerInitializer.scala	Registered iteration handlers
core/amber/src/main/scala/edu/uci/ics/amber/engine/architecture/worker/DataProcessor.scala	Integrated iteration control flow and executor reset
core/amber/src/main/scala/edu/uci/ics/amber/engine/architecture/messaginglayer/OutputManager.scala	Added finalizeIteration API
core/amber/src/main/python/proto/edu/uci/ics/amber/engine/architecture/rpc/init.py	Extended Python protobuf with EndIteration
core/amber/src/main/python/core/runnables/main_loop.py	Handled EndIteration in main loop
core/amber/src/main/python/core/runnables/data_processor.py	Treated EndIteration as InternalMarker
core/amber/src/main/python/core/models/operator.py	Cleared table buffer in on_finish
core/amber/src/main/python/core/models/internal_marker.py	Added EndIteration marker class
core/amber/src/main/python/core/architecture/rpc/async_rpc_handler_initializer.py	Registered Python EndIterationHandler
core/amber/src/main/python/core/architecture/handlers/control/end_iteration_handler.py	Implemented Python EndIteration handler
core/amber/src/main/protobuf/edu/uci/ics/amber/engine/architecture/rpc/workerservice.proto	Added EndIteration/NextIteration RPCs
core/amber/src/main/protobuf/edu/uci/ics/amber/engine/architecture/rpc/controlcommands.proto	Added EndIterationRequest message

Comments suppressed due to low confidence (1)

core/workflow-operator/src/main/scala/edu/uci/ics/amber/operator/sleep/SleepOpDesc.scala:34

• [nitpick] The JSON schema title "n" is ambiguous. Consider using a more descriptive title like "time" or "duration" to clarify the property purpose.

  @JsonSchemaTitle("n")