Remove Humanizer

[geofflamrock]

This PR removes Humanizer, it's a really useful library but the .Humanize() extension methods don't work with AOT, so have replaced them and other usages with direct code. Most of the other usages are pretty simple, the only one is the default branch name which I got GitHub Copilot to write me a reasonable replacement to sanitize branch names. It's also likely to go away in the future.

Fixes #281

Part of a series of PRs that are adding support for AOT:

• Convert to System.CommandLine #276
• Use source generator for Json serialization #285
• Update to Spectre.Console.Cli 0.50.0 #280
• Replaces Octopus.Shellfish with directly using Process #284
• Update to Humanizer.Core v3 beta #286
• Enable publishing with Native AOT #287
• Enable trimming during publish #288
• Remove Humanizer #290
• Update readme to reflect new command options #297
• Remove --working-directory alias #298