This commit adds a unit test for `Srp::Server` (which also covers
`Srp::Client`) building a foundation for writing tests covering edge
cases of SRP server and its interaction with platform "update handler"
callback and SRP client.
For example, the test validates behavior of SRP sever, when
"update handler" accepts, rejects, or ignores (waits for timeout)
the received SRP updates. The test also validates that all heap
allocated objects (used by SRP sever) are properly freed under
different scenarios (validating that there is no heap object leak).
Abtin Keshavarzian