feat: support custom version class override

[binoy14]

Summary

Adds support for a versionClass option in pjson.oclif, allowing CLI authors to provide a custom version class that controls
--version output. This mirrors the existing helpClass override pattern.

• New VersionBase abstract class and default Version implementation in src/version.ts
• loadVersionClass loader that resolves custom classes via string path or {target, identifier} config
• Both --version flag (src/flags.ts) and run() entrypoint (src/main.ts) now use the loader
• Renamed HelpLocationOptions to ClassLocationOptions since it's now shared (deprecated alias kept)
• Exported VersionBase, Version, and loadVersionClass from public API

Usage

{
  "oclif": {
    "versionClass": "./src/my-version"
  }                                                                                                                                      
}

Or with a named export:

  {
    "oclif": {
      "versionClass": {
        "target": "./src/my-version",                                                                                                      
        "identifier": "MyVersion"
      }                                                                                                                                    
    }                                                                                          
  }

[git2gus]

Git2Gus App is installed but the .git2gus/config.json doesn't have right values. You should add the required configuration.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @binoy14 to sign the Salesforce Inc. Contributor License Agreement.