Fix GuessInput focus persistence using StatefulWidget

[harshyadavDeveloper]

Description of what this PR is changing or adding, and why:

Converts GuessInput from a StatelessWidget to a
StatefulWidget to preserve the FocusNode and
TextEditingController across rebuilds.

This ensures _focusNode.requestFocus() works as intended after
submitting input and demonstrates proper lifecycle management for
long-lived objects used by text fields.

The change also adds disposal for the FocusNode and
TextEditingController to avoid resource leaks.

Issues fixed by this PR (if any):

Fixes #13392

PRs or commits this PR depends on (if any):

None.

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[gemini-code-assist]

Code Review

This pull request refactors the GuessInput widget from a StatelessWidget to a StatefulWidget to properly manage the lifecycle of the TextEditingController and FocusNode, including their disposal. A review comment suggests adding a length validation check in the _onSubmit method to ensure that only five-letter guesses are processed, which prevents potential runtime errors when interacting with the underlying game logic.

[harshyadavDeveloper]

Thanks for catching this. I added a length check before submitting guesses so invalid input no longer reaches Word.fromString, preventing crashes while preserving the focus behavior.

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit 54a3f36):

https://flutter-docs-prod--pr13402-fix-guessinput-focus-lifecy-9htefr8i.web.app

[sfshaza2]

lgtm

[sfshaza2]

/gcbrun

[flutter-website-bot]

Staged preview of the updated docs.flutter.dev site (updated for commit 771bb0f):

https://flutter-docs-prod--docs-pr13402-fix-guessinput-focus-l-bb1n29hd.web.app

[sfshaza2]

/gcbrun

[sfshaza2]

@parlough, the build is failing and all it says is that a file needs formatting, but doesn't state which file. Can you assist?