fix: replaced deprecated APIs that was removed in Flutter v3.19

[EdisonModesto]

This PR updates deprecated TextTheme properties that were removed in Flutter v3.19 and above:

Replaced subtitle1 with titleMedium

Replaced headline5 with headlineSmall

These changes align with the new Material 3 naming conventions introduced in Flutter 3.19.

📄 For more details, refer to the official Flutter changelog:
https://docs.flutter.dev/release/breaking-changes/3-19-deprecations

Related Issues: #3

Temporary fix until this PR gets merge:

## remove
#flutter_month_picker: ^0.0.2

## replace with
flutter_month_picker:
   git:
     url: https://github.com/EdisonModesto/flutter_month_picker.git
     ref: main # branch name