Support extensions in nexus-sdk

[brech1]

nexus-vm-prover supports extensions via Machine::<BaseComponent>::prove_with_extensions and verify_with_extensions, but nexus-sdk doesn't expose this.

To use extensions, we have to bypass the SDK and depend on nexus-vm-prover directly, manually handling trace generation, memory layouts, and view construction.

We ran into this issue and did a workaround here:

• feat(nexus): add extensions support eth-act/ere#279