Add simple blender_manifest.toml and __init__.py

[HeyItsBATMAN]

This PR registers a skeleton python script with IO as a simple extension according to the Blender 4.2 extension architecture (meaning an extension that can be packaged, which includes an add-on with the IO functionalities)

This closes #1

Basic IO working

View inside of Preferences -> (Get) Extensions

View inside of Preferences -> Add-ons

Menu entries for importing and exporting

[HeyItsBATMAN]

Notes:

• the manifest currently does not include any maintainers yet, this should be changed to either a single person as a BDFL or multiple persons/organization
• the manifest includes license information now, but this is just the default license from the Blender documentation, and can/should be adjusted according to IIIFs needs
• during importing of the plugin I noticed, that plugin names starting with a numeric value, in this case the 3 of 3d, causes issues when importing, which I solved by locally renaming the package. This is something whe should keep in mind when packaging/deploying Deployment / install process #8
• I added network permissions inside of the manifest, since it will probably be needed for Import a 3D model from URL and preserve URL in Blender data #10