bug(nimbus-fml): Specify dict subtypes for JsonObject in uniffi.toml

[relud]

type dict wasn't enough for cirrus' pyright, it threw

Type of "merge" is "(feature_configs: dict[str, dict[Unknown, Unknown]]) -> MergedJsonWithErrors"

I've confirmed manually that this clears up the issue

I tried to do this originally, but used dict and Any and it didn't work because I didn't realize I needed to use typing.Dict and typing.Any

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • This PR follows the breaking change policy:
    • This PR has no breaking API changes, or
    • There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved
• Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry in CHANGELOG.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due diligence applied in selecting them.

[bendk]

Looks good, just one suggestion. However you want to deal with that is good with me, I don't need to re-review.

[bendk]

You might want to add typing to the imports list. I think this currently works because UniFFI imports typing for its own purposes, but that feels a bit fragile. Double-check me though, I could definitely be wrong about the exact config needed.

[relud]

it causes typing to be imported twice, but it works, and I like not depending on uniffi to implicitly import typing given that it has real potential to not be imported in the future if uniffi doesn't need it