Add `uv tree --show-sizes` to show package sizes (#15531)
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## Summary
Adds the enhancement proposed in #15470. Each package in the dependency
tree now shows its compressed wheel file size, reading the wheel sizes
directly from the lockfile (uv.lock). Doesn't break existing tree
formatting or options. If no wheel size is available, nothing is added.
Now, developers can identify large packages in their dependency tree.
The tree still shows extras exactly as before, and then appends a size
for the package.
## Test Plan
Manually tested :
```
harsh@fcr-node:~/uv/test-uv-tree-sizes$ ../target/debug/uv tree
Using CPython 3.13.7
warning: No `requires-python` value found in the workspace. Defaulting to `>=3.13`.
Resolved 4 packages in 6ms
pure-python v0.1.0
├── click v8.2.1
└── six v1.17.0
harsh@fcr-node:~/uv/test-uv-tree-sizes$ ../target/debug/uv tree --show-sizes
Using CPython 3.13.7
warning: No `requires-python` value found in the workspace. Defaulting to `>=3.13`.
Resolved 4 packages in 6ms
pure-python v0.1.0
├── click v8.2.1 (99.8KiB)
└── six v1.17.0 (10.8KiB)
```
