Add basic tests and benchmarks covering the mac.go file

[onshorechet]

These tests are in prep for a second pull request which will add methods implementing interfaces from the enconding package. The tests were added as a seperate PR in order to verify the new methods match existing functionality.

[onshorechet]

Current bench results:

goos: linux
goarch: amd64
pkg: tinygo.org/x/bluetooth
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkParseMAC-12            37969293                27.50 ns/op
BenchmarkMacToString-12          2137726               566.6 ns/op
BenchmarkUUIDToString-12         9104031               128.8 ns/op
PASS
ok      tinygo.org/x/bluetooth  4.169s