chore(cli): measure performance against wall-clock

[mmastrac]

Fixes test flake by requiring perf to be <150% of wall-clock time rather than <500ms.

[dsherret]

LGTM and good idea! This should stop it from being flaky.

For reference, the flaky test output is:

performanceMeasure => ./cli/tests/unit/performance_test.ts:79:6
error: AssertionError: duration exceeds 500ms: 550.7588259999998
    throw new AssertionError(msg);
          ^
    at assert (file:https:///Users/runner/work/deno/deno/test_util/std/testing/asserts.ts:141:11)
    at file:https:///Users/runner/work/deno/deno/cli/tests/unit/performance_test.ts:105:9

 FAILURES 

performanceMeasure => ./cli/tests/unit/performance_test.ts:79:6