Add CIFuzz Github action

[DavidKorczynski]

Add CIFuzz workflow action to have fuzzers build and run on each PR.

This is a service offered by OSS-Fuzz where rust-lexical already runs (https://github.com/google/oss-fuzz/tree/master/projects/rust-lexical). CIFuzz can help detect regressions and catch fuzzing build issues early, and has a variety of features (see the URL above). In the current PR the fuzzers gets build on a pull request and will run for 300 seconds.