Android: Restore native access to FlutterSecureStorage

[Milad-Akarie]

This PR restores access to FlutterSecureStorage from native Android code.
After the latest update, FlutterSecureStorage is no longer usable on Android from the native side, while iOS remains unaffected.

Use case
The Android app includes an interactive home widget. User actions in the widget trigger network calls that require an auth token stored via FlutterSecureStorage on the Flutter side.

What this PR does
It allows creating and initializing a FlutterSecureStorage instance directly in native Android code and enabling secure token access.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.38%. Comparing base (504c22e) to head (d4a8b7d).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1036   +/-   ##
========================================
  Coverage    99.38%   99.38%           
========================================
  Files            9        9           
  Lines          162      162           
========================================
  Hits           161      161           
  Misses           1        1           

Flag	Coverage Δ
unittests	99.38% <ø> (ø)

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[ethicnology]

@Milad-Akarie do you think your PR can solve #1043 ?