Arm backend: exclude RESCALE from late FuseDuplicateUsersPass

Running FuseDuplicateUsersPass after TOSA lowering fuses value-identical
tosa.RESCALE users of a shared producer onto one node feeding multiple
consumers. Later passes and Vela assume each integer RESCALE feeds a single
consumer, so this miscompiles quantized graphs (observed as all-zero Ethos-U55
output for addmm). The nodes are structurally and quantization-identical, so no
signature refinement can separate them; exclude tosa.RESCALE from fusion
instead. This pass's op-count wins are on TOSA-FP graphs, which carry no
rescales, so the exclusion preserves the intended benefit.

Update the pass test to assert identical RESCALE users are kept separate.

Authored with AI assistance (Claude Code).