gh-37942: Graph constructors: Remove gratuitous nondeterminism
<!-- ^ Please provide a concise and informative title. -->
<!-- ^ Don't put issue numbers in the title, do this in the PR
description below. -->
<!-- ^ For example, instead of "Fixes #12345" use "Introduce new method
to calculate 1 + 2". -->
<!-- v Describe your changes below in detail. -->
<!-- v Why is this change required? What problem does it solve? -->
<!-- v If this PR resolves an open issue, please link to it here. For
example, "Fixes #12345". -->
Since Python 3.x, `dict`s preserve insertion order.
Here we modify the processing of "dict-of-dicts" and "dist-of-lists"
input formats to avoid going through `set`, which introduces gratuitous
nondeterminism regarding the order of vertices.
This change gives for example this improvement:
```sage
sage: G = graphs.CubeGraph(3)
sage: G.vertices(sort=False)
['000', '001', '010', '011', '100', '101', '110', '111']
```
### :memo: Checklist
<!-- Put an `x` in all the boxes that apply. -->
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
### :hourglass: Dependencies
<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - #12345: short description why this is a dependency -->
<!-- - #34567: ... -->
URL: https://github.com/sagemath/sage/pull/37942
Reported by: Matthias Köppe
Reviewer(s): David Coudert, Martin Rubey, Matthias Köppe
