Model the `IndexType` as `uint64_t` when converting to a python integer.
With the python bindings,
```python
DenseIntElementsAttr(op.attributes["attr"])
```
used to `assert` when `attr` had `index` type like `dense<[1, 2, 3, 4]>
: vector<4xindex>`.
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Co-authored-by: Christopher McGirr <christopher.mcgirr@amd.com>
Co-authored-by: Tiago Trevisan Jost <tiago.trevisanjost@amd.com>
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