fix: add hints for Num.to_str and Inspect.to_str errors

[Sim-hu]

Closes #9192
Closes #9191

When a user writes Num.to_str(value) or Inspect.to_str(value), the current error just says the identifier doesn't exist. This adds a hint after the error pointing them to the right syntax:

Num.to_str: suggests method syntax value.to_str()

Inspect.to_str: suggests the renamed function Str.inspect

Follows the existing hint pattern used elsewhere in ModuleEnv.zig (e.g. addAnnotated("Hint:", .emphasized)).

[lukewilliamboswell]

❤️

[lukewilliamboswell]

Did you mean to drop my commits?

I'm not sure why CI failed in that last run, it looks like just the cross-compile runners -- but it's not clear what the issue was. It doesn't look to me like it's related to this change, but there must be something I guess. I'll kick off CI so we can try again without the tests I added.

[Sim-hu]

Sorry about that — I rebased to pick up recent fixes and force-pushed without checking if you'd added commits. Won't happen again.

[github-actions]

Thank you for your contribution! Sometimes PRs end up staying open for a long time without activity, which can make the list of open PRs get long and time-consuming to review. To keep things manageable for reviewers, this bot automatically closes PRs that haven’t had activity in 60 days. This PR hasn’t had activity in 30 days, so it will be automatically closed if there is no more activity in the next 30 days. Keep in mind that PRs marked Closed are not deleted, so no matter what, the PR will still be right here in the repo. You can always access it and reopen it anytime you like!