[Feature] Add shared memory transport and refactor metadata format

[alogfans]

This patch is the first stage of Transfer Engine's code refactoring.

Regarding that in many AI data centers, there are multiple link between two storage medias, we want Transfer Engine to use optimal link to reach higher throughput. E.g., two processes in one machine may use shared memory or nvlink transports.

But the current implementation requires to use EITHER rdma or TCP, which is not suitable for extension. Also, there are many dead code in the transport code. So I plan to refact the metadata & transport impl code to make Transfer Engine more organizable.

Overally, this patch changes the following things:

• Metadata format, see mooncake-transfer-engine/include/segment.h, we also extract some code for coding & decoding segment desc in the seperte file.
• We uniform terms SegmentID and SegmentHandle. In the future, we will remove the term local_server_name and replace it with local_segment_name to avoid ambiguous.
• Add shared memory transports, currently only enable local-to-local data transfer, the remaining part will be fixed at stage 2
• Remove dead code

[alogfans]

This patch is overrided by #170.