Apply env variables to test timeouts consistently

[No9]

The test suite currently defines a session timeout for tests based on process.env.TEST_TIMEOUT
https://github.com/nodejs/llnode/blob/main/test/common.js#L173
This timeout has recently been incremented due to the restricted resources in GH Actions.

The timeout also isn't applied to all the tests and some have been overridden directly in the code base for longer tests.

llnode/test/plugin/workqueue-test.js

Line 29 in ff75da7

t.timeoutAfter(30000);

A suggested approach is to have process.env.TEST_TIMEOUT and a new process.env.TEST_TIMEOUT_LONG consistently applied across the project so that the GH Actions can be incremented without modifying code and local development can shorten a test run by decreasing the same environment variables on the local machine.