Closes https://github.com/astral-sh/ty/issues/453.
## Summary
Add an additional info diagnostic to `unresolved-import` check to hint
to users that they should make sure their Python environment is properly
configured for ty, linking them to the corresponding doc. This
diagnostic is only shown when an import is not relative, e.g., `import
maturin` not `import .maturin`.
## Test Plan
Updated snapshots with new info message and reran tests.
## Summary
Add a new diagnostic hint if you try to use PEP 604 `X | Y` union syntax
in a non-type-expression before 3.10.
closes https://github.com/astral-sh/ty/issues/437
## Test Plan
New snapshot test
This makes an easy tweak to allow our diagnostics for unmatched
overloads to apply to method calls. Previously, they only worked for
function calls.
There is at least one other case worth addressing too, namely, class
literals. e.g., `type()`. We had a diagnostic snapshot test case to
track it.
Closesastral-sh/ty#274
The diagnostic now includes a pointer to the implementation definition
along with each possible overload.
This doesn't include information about *why* each overload failed. But
given the emphasis on concise output (since there can be *many*
unmatched overloads), it's not totally clear how to include that
additional information.
Fixes#274
## Summary
If the user tries to use a new builtin on an old Python version, tell
them what Python version the builtin was added on, what our inferred
Python version is for their project, and what configuration settings
they can tweak to fix the error.
## Test Plan
Snapshots and screenshots:

This makes one very simple change: we report all call binding
errors from each union variant.
This does result in duplicate-seeming diagnostics. For example,
when two union variants are invalid for the same reason.
This does a deeper removal of the `lint:` prefix by removing the
`DiagnosticId::as_str` method and replacing it with `as_concise_str`. We
remove the associated error type and simplify the `Display` impl for
`DiagnosticId` as well.
This turned out to catch a `lint:` that was still in the diagnostic
output: the part that says why a lint is enabled.
We just set the ID on the `Message` and it just does what we want in
this case. I think I didn't do this originally because I was trying to
preserve the existing rendering? I'm not sure. I might have just missed
this method.
In a subsequent commit, we're going to start using `annotate-snippets`'s
functionality for diagnostic IDs in the rendering. As part of doing
that, I wanted to remove this special casing of an empty message. I did
that independently to see what, if anything, would change. (The changes
look fine to me. They'll be tweaked again in the next commit along with
a bunch of others.)