Local task sorting à-la Google Tasks

[opatry]

Description

Compute sorting value for local only tasks reusing Google Tasks logic.

• todo tasks uses index padded by up to 20 0
• completed tasks uses a maximum bound - completion date padded by up to 20 0
• See retro engineering analysis made in Implement task move (local only & remote) #125

Checklist

• I have read the CONTRIBUTING guide
• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing

[github-actions]

Job Summary for Gradle

Build & Test :: build

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
Taskfolio	:tasks-app-desktop:assemble	8.12.1	✅
Taskfolio	:tasks-app-android:assembleStoreRelease	8.12.1	✅
Taskfolio	test :tasks-app-android:testStoreReleaseUnitTest jvmTest	8.12.1	❌
Taskfolio	:tasks-app-android:exportLibraryDefinitions	8.12.1	✅
Taskfolio	:tasks-app-desktop:exportLibraryDefinitions	8.12.1	✅