Add a new Nullable<T> type that deserialize null to Nullable::<T>::Null

[hansl]

Now Option<T> deserializes undefined to None, but keep null as deserialization for the inner type.

This should clarify the API and distinguish between Nullable and Optional when dealing with JavaScript values in the host.

[codecov]

Codecov Report

Attention: Patch coverage is 24.52830% with 40 lines in your changes missing coverage. Please review.

Project coverage is 50.36%. Comparing base (6ddc2b4) to head (23efeee).
Report is 462 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/value/conversions/nullable/mod.rs	23.07%	40 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4325      +/-   ##
==========================================
+ Coverage   47.24%   50.36%   +3.12%     
==========================================
  Files         476      499      +23     
  Lines       46892    49945    +3053     
==========================================
+ Hits        22154    25156    +3002     
- Misses      24738    24789      +51     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[nekevss]

Have some general feedback. It's looking pretty good overall! Had one thought about one of the APIs.

[nekevss]

thought: this may be better as pub fn is<T: PartialEq>(&self)

is_not_null could also be expressed as !v.is_null(), so it seems like a duplicate API, but being able to compare the interior value could be useful.

[hansl]

PartialEq is already implemented for it, so I don't think is is useful. I was trying to add the equivalent of is_some() and is_none() from Option<T>.

[nekevss]

Ah, oops. I didn't mean to leave the PartialEq in there. I meant more so like Gc::is.

Hmmmmm, maybe is_non_null if you were going for a is_some/is_none

[HalidOdat]

Looks good just some minor nitpicky comment 😄

[HalidOdat]

Looks good to me! Just some minor nitpicks 😄