Create a custom `warnings.warn` wrapper that will walk the stack trace
to find the first frame outside of the `gitlab/` path to print the
warning against. This will make it easier for users to find where in
their code the error is generated from

utils.EncodedId() has basically the same functionalityy of using
utils._url_encode(). So remove utils._url_encode() as we don't need
it.

Add EncodedId string class. This class returns a URL-encoded string
but ensures it will only URL-encode it once even if recursively
called.

Also added some functional tests of 'lazy' objects to make sure they
work.

We were using `str.replace()` calls to take care of URL encoding
issues.

Switch them to use our `utils._url_encode()` function which itself uses
`urllib.parse.quote()`

Closes: #1356

Forcing the encoding of '.' to '%2E' causes issues. It also goes
against the RFC:
https://datatracker.ietf.org/doc/html/rfc3986.html#section-2.3

From the RFC:
  For consistency, percent-encoded octets in the ranges of ALPHA
  (%41-%5A and %61-%7A), DIGIT (%30-%39), hyphen (%2D), period (%2E),
  underscore (%5F), or tilde (%7E) should not be created by URI
  producers...

Closes #1006
Related #1356
Related #1561

BREAKING CHANGE: stop encoding '.' to '%2E'. This could potentially be
a breaking change for users who have incorrectly configured GitLab
servers which don't handle period '.' characters correctly.

Move the 'gitlab/tests/' directory to 'tests/unit/' so we have all the
tests located under the 'tests/' directory.