[Spicy-cream]

Summary

Address chenBright's naming review on apache#3535:

• Rename PROTOCOL_RDMA_HANDSHAKE to PROTOCOL_TRANSPORT_HANDSHAKE, keeping value 1.
• Register the common parser as transport_handshake and update the server's always-enabled protocol check.
• Update whitelist coverage and add registration, enum-value, and callback checks.
• Remove the comment retaining the RDMA-specific name.

RDMA-specific wire formats and files, CI workflows, and URMA documentation are unchanged.

Review: apache#3535 (comment)

Validation

• Release static library build passed.
• Common handshake: 28 tests passed.
• Server protocol whitelist: 4 tests passed.
• RDMA: 92 tests passed.
• New protocol-registration test: 100 repetitions passed.
• UBSHM: 43 tests passed on both debugger and normal reruns. The initial suite run segfaulted during shared-memory cleanup; its cause is not established. No UBSHM lifecycle code is changed here.