fix: add the dogstatsd url validator call in dd url tests

[shreyamalpani]

Follow-up to #142, which trimmed trailing slashes from dd_url/url because dogstatsd's DdUrl/DdDdUrl reject a trailing slash with UrlPrefixError. The tests asserted that the trimmed string matched the expected value. This adds dogstatsd::datadog::DdDdUrl::new(...)/DdUrl::new(...) calls to the earlier unit tests, so the tests fail if trim_url ever regresses in a way that still gets rejected by the prefix validator, instead of only checking the trim behavior.

[Copilot]

Pull request overview

This PR strengthens the existing DD_URL / DD_DD_URL trailing-slash trimming unit tests by additionally validating that the trimmed URLs are accepted by dogstatsd’s strict prefix validators (DdUrl / DdDdUrl). This ensures the tests catch regressions where trimming behavior might still leave a value that the downstream validator rejects.

Changes:

• In the DD_DD_URL trailing-slash test, add a dogstatsd::datadog::DdDdUrl::new(...) assertion to ensure the trimmed value passes strict URL-prefix validation.
• In the DD_URL trailing-slash test, add a dogstatsd::datadog::DdUrl::new(...) assertion for the same reason.