feat(rust): add more queries and tests

[tjkirch]

I went through the tree-sitter-rust corpus and added all of the missing statement types that open a new context. I added an example usage of each one to the test file.

I'm new to tree-sitter, but the tests (and some other cases I tried) appear to show the correct context. Some things are debatable - for example, you could make a context for every array expression, but I chose to only do so for ones inside a let declaration, because that gives it a name, and unnamed arrays don't seem to provide as much value. Happy to discuss any of those choices. :)

[tjkirch]

Sorry about the initial CI failure; I didn't initially understand the test that checks nvim-test output. It looks like it's checking that a buffer looks exactly as expected with regard to treesitter, so I updated the expected output to match the actual, since I updated the test file to show off all the new queries. Let me know if that was incorrect, or if I need to test something else.

[lewis6991]

LGTM. Thanks