feat(cache): Calculate size of cache while cleaning

[prady0t]

Description

Small text about the size of cache dirs to be cleaned. Used walkdir for better readability

Fixes #5214

How Has This Been Tested?

Run pixi clean cache

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.
• I have verified that changes that would impact the JSON schema have been made in schema/model.py.

[ruben-arts]

Thanks for working on it; unfortunately, it makes the run significantly slower:

In this minimal example it's not that big of a deal, but cleaning my real cache can take minutes, and doubling that is not worth it. Could you look into how to speed that up?

[prady0t]

Sure. I'll look into it in a few days. This could be a helpful reference: https://github.com/astral-sh/uv/blob/main/crates/uv-cache/src/removal.rs

[baszalmstra]

@prady0t Are you still looking into this?

[prady0t]

@prady0t Are you still looking into this?

Nope. You can go ahead take this.