That's where the mono repo really shines. We have a folder for common stuff that everyone depends upon. A modification is automatically applied/compatible with every micro service. Really streamline the lib updates problem ^^
Most likely CD is intended to mean continuous delivery, which commonly means automation in processes that deliver your software to it’s target audience.
Out of curiosity, how long are CI and CD runs? And are there any particularities in the way of working for example every PR/MR is created by pair programmers, or the use of josh to cut down on time to clone, stuff like that.
If cloning a repo is an issue, you're using CI wrong. --shallow has it's purpose.
Anyway, in my project a complete CI run including local integration tests takes about an hour. We could cut that down by running things in parallel, but we never bothered to add more runners.
I would say, if your tests hold you back, you might want to reconsider testing. Staged testing is an option, or just reevaluate whether you really need all those test cases. Many integration tests are not really testing that much, because 95% of them overlap.