Add an incompatibility that lets pubgrub skip of marker packages when
the base package already has an incompatible version to improve the
error messages (#15199).

The change is also a small perf improvement. Overall this should be able
to improve performance in slow cases by avoiding trying proxy package
versions that are impossible anyway, for a (ideally very small cost) for
tracking the additional incompatibility and tracking the base package
for each proxy package.

```
$ hhyperfine --warmup 2 "uv pip compile --universal scripts/requirements/airflow.in" "target/release/uv pip compile --universal scripts/requirements/airflow.in"
Benchmark 1: uv pip compile --universal scripts/requirements/airflow.in
  Time (mean ± σ):     145.5 ms ±   3.9 ms    [User: 154.7 ms, System: 140.7 ms]
  Range (min … max):   139.2 ms … 153.4 ms    20 runs
 
Benchmark 2: target/release/uv pip compile --universal scripts/requirements/airflow.in
  Time (mean ± σ):     128.7 ms ±   5.5 ms    [User: 141.9 ms, System: 137.3 ms]
  Range (min … max):   121.8 ms … 142.0 ms    23 runs
 
Summary
  target/release/uv pip compile --universal scripts/requirements/airflow.in ran
    1.13 ± 0.06 times faster than uv pip compile --universal scripts/requirements/airflow.in
```

This implementation is the basic version: When we see a proxy
`foo{...}>=x,<y` we add a dependency edge `foo{...}>=x,<y` ->
`foo>=x,<y`. There are several way to extend this, which likely help
more with performance than with error messages.

One idea is that if we see `foo{...}>=x,<y` but we already made a
selection for `foo==z` outside that range, we can insert a dependency
`foo{...}!=z` -> `foo!=z`. This avoids trying any version of the proxy
package except the version that matches our previous selection.

Another is that if we see a dependency `foo>=x,<y`, we also add
`foo{...}>=x,y` -> `foo>=x,<y`. This allows backtracking beyond `foo`
immediately if all version of `foo{...}>=x,<y` are incompatible, since
`foo{...}>=x,<y` incompatible -> `foo>=x,<y` incompatible -> the package
that depended of `foo>=x,<y` is incompatible.

The cost for each of these operations is tracking an additional
incompatibility per virtual package. An alternative approach is to only
add the incompatibility lazily, only when we've tried several version of
the virtual package already. This needs to be weighed of with the better
error messages that the incompatibility gives, we unfortunately have
only few large reference examples.

Requires astral-sh/pubgrub#45

Closes #15199

Add a new method to add a single custom incompatibility that requires
the base package and the proxy package share the same version range.

This intended for cases where proxy packages (also known as virtual
packages) are used. Without this information, pubgrub does not know that
these packages have to be at the same version. In cases where the base
package is already to an incompatible version, this avoids going through
all versions of the proxy package. In cases where there are two
incompatible proxy packages, it avoids trying versions for both of them.
Both improve performance (we don't need to check all versions when there
is a conflict) and error messages (report a conflict of version ranges
instead of enumerating the conflicting versions).

There's several usage patterns for this method. The basic one is upon
encountering a dependency on a proxy package with a range, using this
method with its base package and that range.