V2.11.0 Release - Upgrade to .NET 8

[mukunku]

This PR:

• Upgrades the project to .NET 8 because .NET 7 (and 6) are being retired by the end of this year
• Turns on #nullable enable for the entire solution
• Adds a GitHub Action to run unit tests in PR's
• Cleans up some code and documentation in the repo
• Removes Date Only date formats from the app as they don't seem to be useful
• Help -> About page has a checkbox to create .parquet file association with ParquetViewer now
  • The app will also ask users after they open their 8th parquet file if they'd like to make ParquetViewer their default app for .parquet files if they haven't done so already
• Improves sorting speed & accuracy for Struct, List, Map, and byte[] types
• When a column is sorted, the app will now widen the column to try make sure the sorting arrow is shown

[github-actions[bot]]

Unit Test Results

✔️ Tests 18 / 18 - passed in 2.7s 🔍 click here for more details
✏️ updated for commit 70ca1a9