Fix FuseInitializersTransformer consumer input lookup (#32426)
## Description
Fixes #32405.
`FuseInitializersTransformer` locates the consumer input to replace by
comparing the producer node name with consumer input value names. ONNX
does not require node names and output value names to match.
When they differ, the lookup can reach the end of `InputDefs()` and the
following access can go out of bounds.
The transformer now matches the consumer input against the Cast node's
output value name and guards against an unexpected missing match.
## Tests
Adds a regression test where the Cast node name differs from its output
value name, matching the failure reported in #32405.