[Refactoring] Separate worker and manager class

[chaeyoung-lee]

This PR is mainly about separating the worker module from the monolithic Agora class.

Summary

• Separate worker module from Agora class in worker.cc, worker.h
• Defines structs for inter-class communication of messages and data in agora_helper.h
• Misc. cleanup of Agora class (commit 179786f, 3c36f85)

Moving Forward

Sprint	Description	Dates	Components
1	Separation of worker and manager class	7/21-8/10	manager, worker
2	Separation of knowledge from logic in scheduling	9/1-9/16	manager
3	Task abstraction	9/19-10/3	doer, network threads

[chaeyoung-lee]

Major changes after @733c2b9 (Andrew's review)

• Dead code removed, location changes in minor function definitions
• Constructed AgoraBuffer class that stores buffers shared among the manager and the workers. Most of its members are private and can be accessed through Get/Set functions.

// agora.h
std::unique_ptr<AgoraBuffer> buffer_;

// agora.cc: construction of Agora manager class
Agora::Agora(Config* const cfg)
    : buffer_(std::make_unique<AgoraBuffer>(cfg)), ... { ... }

// agora.cc: example of accessing buffer class members
const auto* pkt = reinterpret_cast<const MacPacketPacked*>(
              &buffer_->GetDlBitsBuffer(ue_id)[radio_buf_id *
                         config_->MacBytesNumPerframe(Direction::kDownlink)]);

An exception is network buffers. Changing how PacketTxRx class stores and loads data from the network buffers result in conflicts with the PhyUe class in the client side. Therefore, as of now, we leave such network buffers as public members of the AgoraBuffer class.

class AgoraBuffer {
 public:
  // TX RX Buffers
  // Direct access is allowed for packetTXRX classes
  Table<char> socket_buffer_;
  char* dl_socket_buffer_;
  Table<complex_float> calib_ul_buffer_;
  Table<complex_float> calib_dl_buffer_;