Add scenario tests for pip-compile (#1011)

e.g. for scenarios that test resolution _without_ installation.

This refactors the `update` script to generate scenario test files for
`pip compile` _and_ `pip install`. We don't overlap scenarios to save
time. We only generate `pip compile` test cases for scenarios we cannot
represent with `pip install` e.g. a `--python-version` override.

The _one_ scenario I added happened to reveal a bug in our resolver
where we were incorrectly filtering versions by the installed version
when wheels were available. Per the comment at
https://github.com/astral-sh/puffin/issues/883#issuecomment-1890773112,
we should _only_ need to check for a compatible installed Python version
when using a different _target_ Python version if we need to build a
source distribution.
53bce68400
resolves this by removing the excessive constraints — the correct Python
version incompatibilities are applied elsewhere.

crates/puffin-resolver/src/resolver/mod.rs

@@ -652,22 +652,6 @@ impl<'a, Provider: ResolverProvider> Resolver<'a, Provider> {
                     self.visit_package(package, priorities, request_sink)?;
                 }
 
-                // If a package has a `requires_python` field, add a constraint on the target
-                // Python version.
-                if let Some(requires_python) = metadata.requires_python.as_ref() {
-                    let version = requires_python
-                        .iter()
-                        .map(PubGrubSpecifier::try_from)
-                        .fold_ok(Range::full(), |range, specifier| {
-                            range.intersection(&specifier.into())
-                        })?;
-                    constraints.insert(
-                        PubGrubPackage::Python(PubGrubPython::Installed),
-                        version.clone(),
-                    );
-                    constraints.insert(PubGrubPackage::Python(PubGrubPython::Target), version);
-                }
-
                 // If a package has an extra, insert a constraint on the base package.
                 if extra.is_some() {
                     constraints.insert(