test framework: Implement ProxyGetProperty and ProxySetProperty

[jmjolysc]

Hello there,

Currently, the ProxyGetProperty and ProxySetProperty methods are not implemented in proxytest. This prevents developers from writing more complete unit tests. Would you consider the implementation of those methods as a feature improvement?

When looking at the code, one approach could be adding a map (maybe string or []byte to []byte) in the hostEmulator data structure of the proxytest package, in order to store the state of properties. If you also think that's a straightforward approach, would you like me to give it a try and submit a pull request?

Thank you.

[mathetake]

sg! I would appreciate it if you could give it a shot. Thanks!