Changed integrator render functions to take UInt32 for seed

[DoeringChristian]

Description

The PR expands on Change seed function to take drjit type for seed, by changing the render, render_forward and render_backward signatures to take a UInt32 for the seed argument as well.
This is necessary for function freezing, to allow changing the seed between calls to a frozen function without having to re-trace it.

Testing

Checklist

• My code follows the style guidelines of this project
• My changes generate no new warnings
• My code also compiles for cuda_* and llvm_* variants. If you can't test this, please leave below
• I have commented my code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I cleaned the commit history and removed any "Merge" commits
• I give permission that the Mitsuba 3 project may redistribute my contributions under the terms of its license

[merlinND]

Hi @DoeringChristian,

Could you please rebase this PR, let's check if the CI is still green, and then I think it should be okay to merge.

[DoeringChristian]

Let me check, this PR might be included in the frozen-functions one. Might be easier to merge it in one go.

[merlinND]

Personally I like having a smaller PR just for this change, especially given that the other PRs are huge. (Assuming that this PR is works correctly on its own).

[wjakob]

Thanks @DoeringChristian, I'll merge this PR without further review since the changes seem rather harmless.