[Issue #4] Make writng of DataFrames more flexible

[GKrivosheev-rms]

• Added overload extension with ability to write an IEnumerable<DataFrame> to a single file
• Add ability to write DataFrame re-entrrantly to the same file
• Make Nullability of columns depending on underlying type (stable despite changes to row data)

[adamreeve]

Thanks for the PR, the approach looks good to me but I've left a couple of comments with some things that need addressing.

Just a note about code formatting, our format check that runs in CI doesn't currently show the changes required, but you can manually run the formatter before committing to make sure the format will be compatible with:

dotnet tool restore
dotnet jb cleanupcode --profile="Built-in: Reformat Code" --settings="ParquetSharp.DataFrame.DotSettings" --verbosity=WARN "ParquetSharp.DataFrame" "ParquetSharp.DataFrame.Test"

[adamreeve]

Hi @GKrivosheev-rms, are you planning on following through with this PR? I think this feature would be quite useful so I'm happy to take over completing this change if you no longer have the time for this.