Audit and convert tests to test/unit (minitest)

:construction: WIP :construction: 

This PR converts the RSpec tests to minitest. Most of the tests were translated over, but I'll make inline notes where I modified or removed tests for clarity.

- convert rspec tests to test/unit
- rename 'test/common' to 'test/test_helper'
- remove metaid dependency
- remove rspec dependency
- remove autotest
- auto generate gemspec files manifest

@jch yeah, it's not obvious at first, but any time a `search` (or any other) operation is run without an open connection (so, normal operation), it calls a `bind` by default, but only on `Net::LDAP::Connection`, not the higher level `bind`, so it's *vital* to have the lower level event tracked, and useful to differentiate implicit and explicit binds.

Happy to help with the "weirdness"; what is is that you saw? (I'm sure I'll see it if I run these tests/look at the CI output.) Nothing looks out of the ordinary at first glance.