Use literal unions in python enum codegen (#6408)

### What

Strings now autocomplete in places where we use enum classes that get
converted from strings.

Follow up to #6407

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/6408?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/6408?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!

- [PR Build Summary](https://build.rerun.io/pr/6408)
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

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crates/re_types_builder/src/codegen/python/mod.rs

@@ -847,7 +847,12 @@ fn code_for_enum(
  }
  }
 
- code.push_unindented(format!("{name}Like = Union[{name}, str]"), 1);
+ let variants = obj
+ .fields
+ .iter()
+ .map(|v| format!("Literal[{:?}]", v.pascal_case_name().to_lowercase()))
+ .join(" | ");
+ code.push_unindented(format!("{name}Like = Union[{name}, {variants}]"), 1);
  code.push_unindented(
  format!(
  r#"

examples/python/blueprint_stocks/blueprint_stocks.py

@@ -115,7 +115,7 @@ def style_peak(symbol: str) -> rr.SeriesPoint:
  return rr.SeriesPoint(
  color=0xFF0000FF,
  name=f"{symbol} (peak)",
- marker="Up",
+ marker="up",
  )