Support extra_args

[MisanthropicBit]

This PR adds support for neotest.RunArgs.extra_args passed to build_spec for adding additional arguments to the test process via neotest.run.run.

An example use case is running tests and updating snapshots:

require("neotest").run.run({ extra_args = { "--updateSnapshots" } })

Other changes

• I fixed the is_test_file tests that weren't run asynchronously but was calling async functions.
• Updated tests after path escaping in fix: escape test file path #109. I'm not sure why they were passing before. There is also no test output from the test script in github actions so there might be something amiss with the setup.

[izifortune]

This will indeed be helpful

[MisanthropicBit]

@izifortune FYI, I've started a new dev branch on my fork that I intend to keep in sync with the upstream repo and continuously merge select open PRs so I can start using some of these things myself until upstream catches up.