Ensure the results directory exists when writing a file in AllureRuntime

[delatrie]

AllureRuntime creates the results directory only once (in its constructor).
Some testing tools like Cypress support interactive testing with long-running sessions. If the directory gets deleted, each further attempt to write an Allure file will fail until the directory is recreated by hand or until the tool is restarted.

We should check if the directory exists before writing a file. If it's not, we should create it.

Originally posted by @delatrie in #815 (comment)