Always treat paths after -e as directories

[charliermarsh]

Summary

Closes #16582.

[charliermarsh]

It looks like missing_editable_file regressed a bit.

[codspeed-hq]

CodSpeed Performance Report

Merging #16967 will not alter performance

_{Comparing charlie/err (2688a12) with main (2abe56a)}

Summary

✅ 5 untouched

[konstin]

This creates an unintuitive error message downstream: If I have a directory my.project.whl and

-e my.project.whl

I get:

$ uv  pip install -r requirements.txt
error: The wheel filename "my.project.whl" is invalid: Must have a version

If I use a valid wheel filename as the directory name, it accepts it, build the directory, but expects the output to conform to the wheel filename:

-e my_project-0.1-py3-none-any.whl

my_project-0.1-py3-none-any.whl/pyproject.toml:

[project]
name = "foo"
version = "0.1.0"

$ uv pip install -r requirements.txt 
  × Failed to build `my-project @ file:///home/konsti/projects/uv/debug/my_project-0.1-py3-none-any.whl`
  ╰─▶ Package metadata name `foo` does not match given name `my-project`

I could see that kind of directory name be created by using some unzipping tool on a wheel.

On a sidenote, it only checks the package name, while ignoring version mismatches, so the following installs successfully:

[project]
name = "my_project"
version = "1.2.3"