Fix DeepCompile+Z3 on PyTorch v2.9/2.10

[tohtana]

DeepCompile+Z3 didn't work with PyTorch v2.9/2.10 because:

• PyTorch v2.9+ started enforcing stricter TorchDynamo parameter tensor-match guards. During DeepCompile tracing, some ZeRO-3 parameters were temporarily all-gathered, so Dynamo recorded full sizes such as 4096
• By the time guard evaluation ran, DeepSpeed had already released those params back to the normal ZeRO-3 partitioned representation, where param.data is empty(0). That produced guard failures like expected 4096, actual 0.

This PR resolves the issue by:

• Leep full-shape dummy tensors for symbolic tracing
• Override guard size/stride metadata for ZeRO-3 params to the stable released representation instead of transient gathered sizes

This PR also includes fixes of these bugs:

• For v2.7 and v2.8, the compiled backward graph could hoist end_backward ahead of the real reduce_grad calls. - Selective unsharding pass can overcount the persistence memory budget.

Note: DeepCompile is still incompatible with v2.11. It will be addressed by another PR.

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