fix(ui_auth, ui_storage): don't call setState after dispose in ProfileScreen, DeleteAccountButton and UploadButton

[BurningAXE]

Description

Follow-up to #720, which fixed the same bug in ForgotPasswordView.

Several widgets await a Firebase call or a dialog and then call setState without checking mounted, often in a finally block. If the widget leaves the tree while the await is pending (the screen is popped, or a parent rebuilds without it), that setState runs on a disposed State:

• Debug: setState() called after dispose(): …
• Release: the assertion is compiled out, so State.setState reaches _element!.markNeedsBuild() and throws Null check operator used on a null value.

Affected sites:

Widget	After which await
DeleteAccountButton	currentUser.delete() (finally). The existing if (!mounted) return; inside try doesn't skip finally, so the crash still happens on the success path
DeleteAccountButton	the confirmation dialog / deleteConfirmation, and the retry after onSignInRequired. After a requires-recent-login error it also called onSignInRequired itself, and ProfileScreen's implementation looks up localizations with its own defunct context
ProfileScreen (linked providers)	unlink() + reload(), in the success path, catch and finally
ProfileScreen (MFA toggle, disable)	getEnrolledFactors(), and unenroll() in the success path, catch and finally. On a recent-login error it also opened the re-authentication dialog with the disposed context, then retried _disable()
ProfileScreen (MFA toggle, enable)	enroll() in the CredentialReceived action (success path, catch, finally), and the final setState after startPhoneVerification returns. The finally also pops until the profile screen's route; if that route has been removed, popUntil never finds it and pops every route, so it now checks currentRoute.isActive first
UploadButton (firebase_ui_storage)	the upload task (finally)

The fix uses the usual pattern:

• After an await, if (!mounted) return; before touching the State. If the widget is gone before a follow-up step starts, that step is skipped: deleting after confirmation, unenrolling after the factor lookup, asking to re-authenticate (onSignInRequired, the MFA re-authentication dialog), retrying, or rebuilding through onToggled / onProviderUnlinked. Those rebuild callbacks target a RebuildScope that went away with the widget.
• setState inside catch / finally is wrapped in if (mounted). The rest of those blocks still runs. For example, the MFA enrolment finally still pops the phone verification route, and UploadButton still calls onUploadComplete / onError.

Tests

• test/widgets/delete_account_button_test.dart (new, 4 tests)
• test/screens/profile_screen_test.dart (new, 12 tests)
• firebase_ui_storage/test/upload_button_test.dart (new, 1 test; skipped on web because XFile.readAsBytes can't be faked through the file_selector method channel)

Each test disposes the widget while the await is pending, then completes it. All 17 fail on main and pass with this change. Most fail with setState() called after dispose() or an equivalent error, and the rest because the follow-up step still ran. I also turned each of the 17 new mounted checks, and the isActive check, off one at a time, and every one made at least one test fail.

ProfileScreen tests dispose the MFA toggle under an open dialog / phone verification route by re-pumping the screen with showMFATile: false, so the route stack (and popUntil) stays intact.

Related Issues

None found. #720 fixed the same pattern in ForgotPasswordView. #353 was another case of it, in EmailVerificationBadge. Open PR #279 touches DeleteAccountButton and ProfileScreen too, but in different lines.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///). (n/a: no public API change)
• The analyzer (melos run analyze) does not report any problems on my PR.
• All unit tests pass (melos run test:unit:all doesn't fail).
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces mounted checks across several stateful widgets (_LinkedProvidersRowState, _MFAToggleState, _DeleteAccountButtonState, and _UploadButtonState) to prevent calling setState or executing callbacks after the widgets have been disposed. It also adds comprehensive unit tests to verify that these widgets handle unmounting gracefully during asynchronous operations. The review feedback suggests two important safety improvements: adding a mounted check in delete_account_button.dart before invoking onSignInRequired and the recursive _deleteAccount call, and checking mounted in profile_screen.dart before popping the navigation stack to avoid potential crashes if the route is no longer present.