tools: pin GR push-buffer window from guest pagemap per boot; widen injected-pin table

The GR channel GPFIFO entries point at pushes in the client GPU VA window
(observed 0x200400000 + stride, one allocation per channel) and the pump
cannot read them: pushes_nomap grows and the tracking-semaphore releases
they carry never land. The pushes are sysmem pages mapped into the client
process, so /proc/<pid>/pagemap in the guest gives the GPA.

New guest helper guest_pmap_win.py batch-reads the pagemap of a VA range
(512 entries per pread). New host tool pin_gr_window.py rescans the window
on an interval, follows cdt pid changes, and injects VA->PA runs through
sema_map_add (same mechanism as the counters and the CE pushbuffer pins).
The injected-pin table grows 8k -> 32k slots so the CE pushbuffer (4096)
plus the GR window pages fit without drops.

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