fix: remove vim.validate

Closes #24

feat(lsp): add supports_method to lsp client (#21)

chore: styling

fix(tasks): gracefully handle callbacks after cancel

If a callback returns after a task is already cancelled, we should
gracefully handle it by not attempting to set the result of the task
since it is already set.

See #15

chore: styling

fix(tasks): cancel immediately

Previously the loop would wait for the next yield but instead we can
just step forward immediately when cancelling.

See #15

tests: remove old test

test(process): fix exit code test

feat(tests): port changes from neotest/nio

feat: file module