Hint at missing project.name

[konstin]

We got user reports where users were confused about why they can't use [project.urls] in pyproject.toml (i think that's from poetry?). This PR adds a hint that (according to PEP 621), you need to set project.name when using any project fields. (PEP 621 also requires project.version xor dynamic = ["version"], but we check that later.)

The intermediate parsing layer to tell apart syntax errors from schema errors doesn't incur a performance penalty according to epage (toml-rs/toml#778 (comment)).

Closes #6419
Closes #6760

[konstin]

We only have name/version/dynamic here with the last two being optional, so we skip the check that's it's actually name here (in the other case we have to check for name to not confuse it with e.g. invalid project.dependencies; it's only a heuristic but imho good enough for the error hinting path)

[jooon]

This hint seems to only be shown when a project is explicitly built.

$ cat pyproject.toml
[project.urls]
repository = 'https://github.com/octocat/octocat-python'
$ cargo run -- pip install .
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.20s
     Running `/home/jon/src/github.com/astral-sh/uv/target/debug/uv pip install .`
error: Failed to extract static metadata from `pyproject.toml`
  Caused by: `pyproject.toml` is using the `[project]` table, but the required `project.name` is not set.
  Caused by: TOML parse error at line 1, column 2
  |
1 | [project.urls]
  |  ^^^^^^^
missing field `name`

Not, when it is just parsed because of uv run.

$ cargo run -- run python
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.20s
     Running `/home/jon/src/github.com/astral-sh/uv/target/debug/uv run python`
error: Failed to parse: `pyproject.toml`
  Caused by: TOML parse error at line 1, column 2
  |
1 | [project.urls]
  |  ^^^^^^^
missing field `name`

[konstin]

This is modelled after #6419 and #6760, where the failing cases were dependencies, not the project itself

[charliermarsh]

@konstin -- Do you think we can also add this for the workspace discovery errors?

[charliermarsh]

I extended it to uv run in #7399.