fix: correctly identify the target inside packages and match output

[duncanawoods]

This is a PR to fix most of #18955

The two main changes:

1. update request::handle_run_test and test_runner to identify the target inside a package that matches a test request. This fixes RA failing to find the right package because the test uses the target name.

2. extend CargoActor to take a parser object rather than just a generic type with static parsing functions. This allows context about the invocation of cargo to be used when interpreting the cargo output so it can be properly integrated with the GUI.

In this case, it's information about the test that has been run which isn't contained in cargo output. The current behaviour is very flaky so that if you have tests with the same name in multiple crates or targets, the results are often assigned to the wrong target.

The StatelessParser wrapper ensures existing static parsers can be used without any changes.

[duncanawoods]

This fixes 1 a), 1 b) and 2. from the issue.

1 c) requires more thought / discussion:

• changing the test_runner to launch multiple cargo test processes would be significant behaviour change
• introducing the notion of a default target or setting deserves some thought