Addresses panic introduced in #2596 and reported in #2763 (comment)

When there are multiple versions of a package available, we remove the existing packages before installing the resolved version to "fix" the environment. We must remove all of the package versions and reinstall because removing any of the package versions could break the others. Since reinstalls require a pull from the remote, this broke a contract between the resolver and the planner which must always agree on which packages should come from the remote. This further demonstrates that we should be constructing the install plan with more concrete knowledge from the resolver (i.e. ResolvedDist instead of Requirement) to avoid having to manually ensure logic matches.

Test plan

Fails on main with panic succeeds on branch

uv venv --seed
source .venv/bin/activate
pip install anyio==3.7.0 --ignore-installed
pip install anyio==4.0.0 --ignore-installed
cargo run -- pip install anyio black -v