Expose more fine-grained control for uv sync command

[Vigilans]

uv sync can be roughly divided into three steps:

1. Sync venv (uses project.requires-python in pyproject.toml)
2. Sync dependencies (uses project.dependencies in pyproject.toml)
3. Install project

User may demand more specific behaviors in the sync process. For example:

1. User may only want to sync venv. (Create a venv based on current project's project.requires-python in pyproject.toml)
2. User may only want to sync venv and install the dependency, but do not install the project. (Allow users to install a project's dependencies, without the project itself #4028, Feature request: add a way to install only build dependencies #1516)
3. User may want to fully sync the environment, but install the project in editable mode.

---

Example 2 and 3 can be achieved with workaround if we have 1:
2. Use uv pip install -r pyproject.toml on the synced venv.
3. Use uv pip install -e . on the synced venv.

I would like to know do we have a way to only create venv based on requires-python in pyproject.toml?

[zanieb]

To respond in part: I think, in the future, uv venv will respect the pyproject.toml by default.