Fix GuestDataPool lease leak on non-GPU compute dispatch paths (#759)

ObserveComputeDispatch only returned evaluation's pooled arrays when
evaluationHandledByCpu was set. Dispatches rejected before submission
(empty resource tables, oversized workgroup, compile failure) or a
compute submit that got dropped instead of enqueued (workSequence == 0)
never handed those buffers to a consumer that would return them,
leaking one lease per occurrence and growing GuestDataPool.Shared
without bound over a long session.

Adds GuestDataPool.DiagnosticStats() (outstanding lease count, idle
cached bytes) surfaced in the periodic [LOADER][PERF] line, to catch
this class of regression going forward.

Verified on Ghost of Yotei and Demon's Souls: pool_leases grew
unbounded before the fix (525 in 5 min on Demon's Souls, 1114 in 180s
on Yotei) and stays flat/bounded after (0-6 and 2-18 respectively),
with no behavioral regression observed.

src/SharpEmu.Libs/Agc/AgcExports.cs

@@ -11307,7 +11307,9 @@ public static partial class AgcExports
             }
         }
 
-        if (evaluationHandledByCpu)
+        // Rejected/CPU-handled dispatches never hand evaluation's pooled buffers to a
+        // consumer that would return them; reclaim here to keep GuestDataPool.Shared bounded.
+        if (evaluationHandledByCpu || !gpuDispatch)
         {
             ReturnPooledEvaluationArrays(evaluation);
         }