[Feature] Follow up on #162: sparse tensor SSD offload and io_uring

[xupinjie]

Background

PR #162 introduced SSD offload for SimpleStorage. Two suggestions from its review were deferred to follow-up PRs.

Follow-up work

• Support SSD offload for sparse tensors, which currently remain in host memory.
• Evaluate existing io_uring libraries and add io_uring support for SimpleStorage SSD I/O, with benchmarks against the current implementation.

Related PR: #162