withBuiltChild fix

[subzero911]

I fixed Observer.withBuiltChild constructor.
I removed runtime asserts and unneeded nullables. So now it's neat.

I also added an example to the docs.

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Pull Request Checklist

• If the changes are being made to code, ensure the version in pubspec.yaml is updated.
• Increment the major/minor/patch/patch-count, depending on the complexity of change
• Add the necessary unit tests to ensure the coverage does not drop
• Update the Changelog to include all changes made in this PR, organized by version
• Run the melos run set_version command from the root directory
• Include the necessary reviewers for the PR
• Update the docs if there are any API changes or additions to functionality

[subzero911]

@pavanpodila @amondnet

[subzero911]

@pavanpodila
CI/CD says don't use explicit types for constructor super parameters. But I see nothing bad with it. You'd better set less strict linter rules.

[pavanpodila]

@pavanpodila

CI/CD says don't use explicit types for constructor super parameters. But I see nothing bad with it. You'd better set less strict linter rules.

I'm using default rules with no overrides. These are the ones recommended by Flutter itself

[pavanpodila]

We should also upgrade the lints packages

[subzero911]

It isn't shown as an error in the IDE, but CI/CD fails on this line for some reason.

[pavanpodila]

let's remove the type and try ?

[subzero911]

Anyway, it's out of scope of the current MR. It should be done in a separate MR.

[subzero911]

@pavanpodila are you crazy?
Why did you close this PR?!
I waited for 2 weeks to merge it!!!