Rename directory argument

https://github.com/linksplatform/IO/blob/164fc97bf604de486fbbbee8465fa0e9543f2def/csharp/Platform.IO/FileHelpers.cs#L288

We should use `path` instead of old name.

See [Directory.EnumerateFiles method in the .NET documentation](https://docs.microsoft.com/en-us/dotnet/api/system.io.directory.enumeratefiles?view=net-5.0#System_IO_Directory_EnumerateFiles_System_String_System_String_System_IO_EnumerationOptions_).

After this change comments to these methods can be simplified.

Open csharp/Platform.IO/FileHelpers.cs at the linked location and inspect the referenced methods and their comments. Rename the directory argument to path, simplify the comments as requested, and run the repository's existing checks to confirm the change is complete.

Written by the indexing model from the issue text.