Remove extraneous installations in uv sync by default

[ibraheemdev]

Summary

First step of #4358. uv sync will now remove any extraneous installations by default.

[ibraheemdev]

As a reference point, Poetry makes this opt-in, with poetry install --sync. However, exact sync by default with an opt-out seems like the correct default for uv sync.

When you omit the --sync option, you can install any subset of optional groups without removing those that are already installed. This is very useful, for example, in multi-stage Docker builds, where you run poetry install multiple times in different build stages.