Add XPU support in Tensorpipe.

[kpjeeja]

add Xpu basic channel and Xpu event-driven runtime support

Adds initial Xpu device support:

- Xpu_basic channel: async CPU↔Xpu and Xpu↔Xpu transfers
- XpuLoop: event-driven progress engine (Xpu events + worker thread)
- XpuBuffer: wraps Xpu device memory
- Xpu.h: device traits, helpers, and event utilities

This provides an async Xpu backend suitable for RPC, without IPC or
Xpu-specific high-performance channels.

Signed-off-by: Jeeja KP <jeeja.kp@intel.com>

[meta-cla]

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