prototype: --name to direct to a project from anywhere

[ruben-arts]

Prototyped this to align more with conda like tools.

~ via 🐍 v3.11.10 via 🦀 v1.80.0 
❯ pixi init registered_project --register
✔ Created /home/rarts/registered_project/pixi.toml
✔ Registered project 'registered_project' to be used from anywhere by name.

~ via 🐍 v3.11.10 via 🦀 v1.80.0 
❯ pixi add python --name registered_project
✔ Added python >=3.13.0,<3.14

~ via 🐍 v3.11.10 via 🦀 v1.80.0 
❯ pixi run --name registered_project "echo \$PIXI_PROJECT_MANIFEST"
/home/rarts/registered_project/pixi.toml

~ via 🐍 v3.11.10 via 🦀 v1.80.0 
❯ pixi shell --name registered_project

~ via 🐍 v3.13.0 via 🦀 v1.80.0 via 🅒 registered_project 
❯ 

Let me know what you think of this.

[synapticarbors]

As you might imagine, I'm super excited about this. I played with it a little bit and had some initial feedback:

• I didn't see it in the current draft, but one useful thing to have would be a way to list all registered projects along with maybe where in the filesystem they reside.

• It looks like there isn't any protection against registering projects with the same name in different locations. It just overwrites the former without any warning:

❯ ~/Projects/github/pixi/target/release/pixi init foo --register
✔ Created /Users/xyz/opt/pixienvs/foo/pixi.toml
✔ Registered project 'foo' to be used from anywhere by name.
❯ cd ~/Desktop
❯ ~/Projects/github/pixi/target/release/pixi init foo --register
✔ Created /Users/xyz/Desktop/foo/pixi.toml
✔ Registered project 'foo' to be used from anywhere by name.
❯ bat ~/.pixi/config.toml
───────┬───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: /Users/xyz/.pixi/config.toml
───────┼───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ detached-environments = false
   2   │
   3   │ [registered-projects]
   4   │ foo = "/Users/xyz/Desktop/foo/pixi.toml"