feat(server): raise receive pool default to 128 GiB

[ketor]

Summary

• raise the default DFKV_RDMA_RECV_SEGMENT_SIZE hard budget from 16 GiB to 128 GiB
• keep lazy 256 MiB initial/incremental commitment; explicit operator overrides remain unchanged
• update server help, deployment/connector docs, README, changelog, and RDMA fixture commentary
• bump root and connector package versions to 2.24.2

Validation

• built dfkv_server, rdma_recv_segment_test, and rdma_loopback_test with RDMA+io_uring enabled
• rdma_recv_segment_test: 10 passed
• rdma_loopback_test: 22 passed, 55 hardware-dependent skipped
• dfkv_server --help reports default 128 GiB
• dfkv_server --version reports 2.24.2 after reconfigure
• locally built dfkv_common/dfkv_connector/dfkv_vllm 2.24.2 wheels