Add coder fuzz tests to the Go SDK

With the Go SDK now on minimum Go version 1.18, fuzz tests can be added to the test corpus. The coder package is a good place to start with this, as we handle primitives that can be directly generated by Go's native fuzz testing and can check that we are getting the same values out after encoding and decoding. 

An overview of potential fuzz testing in the Beam Go SDK can be found here: https://docs.google.com/document/d/1VHe5xFHjsmgOj2upH2k4zT90S5SCPtGYSJNcvPj5fig/edit?usp=sharing