Upgrade Dart/Flutter SDK and Dependencies

[rodiguif]

Description ✍️

This PR introduces the following updates:

• Adds a .tool-versions file to pin development environment tools:
  • flutter 3.32.8
  • dart 3.8.1
• Updates pubspec.yaml to bump key dependencies:
  • intl from ^0.19.0 → ^0.20.2
  • rxdart from ^0.27.7 → ^0.28.0
  • collection from ^1.18.0 → ^1.19.1

Overview 👀

These updates ensure compatibility with the latest Flutter SDK and help maintain stability with newer versions of core packages.

No functional or visual changes are expected.

How to Smoke?

1. Run asdf install (if using asdf) to apply the pinned versions.
2. Run flutter pub get to fetch updated dependencies.
3. Ensure the app builds and runs without issues using the new SDK and package versions.