This PR revamps how errors in signia are handled.
This was brought about by a situation that @MitjaBezensek encountered
where he added a reactor to a shape util class. During fuzz tests, that
reactor was being executed at times when the Editor was not in a usable
state (we had a minor hole in our sync rebase logic that allowed this,
fixed elsewhere) and the reactor was throwing errors because it
dereferenced a parent signal that relied on the page state
(getShapesInCurrentPage or whatever) when there were no page records in
the store.
The strange part was that even if we wrapped the body of the reactor
function in a try/catch, ignoring the error, we'd still see the error
bubble up somehow.
That was because the error was being thrown in a Computed derive
function, and those are evaluated independently (i.e. outside of the
reactor function) by signia as it traverses the dependency graph from
leaves to roots in the `haveParentsChanged()` internal function.
So the immediate fix was to make it so that `haveParentsChanged` ignores
errors somehow.
But the better fix involved completely revamping how signia handles
errors, and they work very much like how signia handles values now. i.e.
- signia still assumes that deriver functions are pure, and that if a
deriver function throws once it will throw again unless its parent
signals change value, so **it caches thrown errors for computed values**
and throws them again if .get() is called again before the parents
change
- it clears the history buffer if an error is thrown
- it does not allow errors to bubble during dirty checking i.e. inside
`haveParentsChanged` or while calculating diffs.
### Change Type
- [x] `patch` — Bug fix
- [ ] `minor` — New feature
- [ ] `major` — Breaking change
- [ ] `dependencies` — Changes to package dependencies[^1]
- [ ] `documentation` — Changes to the documentation only[^2]
- [ ] `tests` — Changes to any test code only[^2]
- [ ] `internal` — Any other changes that don't affect the published
package[^2]
- [ ] I don't know
[^1]: publishes a `patch` release, for devDependencies use `internal`
[^2]: will not publish a new version
### Test Plan
1. Add a step-by-step description of how to test your PR here.
2.
- [x] Unit Tests
- [ ] End to end tests
### Release Notes
- Add a brief release note for your PR here.
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