Fix encounter drug order performance issues

[isaacmujuni]

Description of what I changed

I fixed performance and null pointer issues in the Drug Order API. I optimized the active order queries to only fetch drug orders when saving drug orders, eliminating unnecessary database queries. I also added proper null checks in failOnOrderTypeMismatch and areDrugOrdersOfSameOrderableAndOverlappingSchedule methods to prevent potential null pointer exceptions. Additionally, I added comprehensive test coverage to verify the performance optimization works correctly.

Issue I worked on

This addresses performance issues in drug order conflict checking and potential null pointer exceptions in OrderService validation methods.

Checklist: I completed these to help reviewers :)

• [x] My IDE is configured to follow the code style of this project. No? Unsure? -> configure your IDE, format the code and add the changes with git add . && git commit --amend
• [x] I have added tests to cover my changes. (If you refactored existing code that was well tested you do not have to add tests) No? -> write tests and add them to this commit git add . && git commit --amend
• [x] I ran mvn clean package right before creating this pull request and added all formatting changes to my commit. No? -> execute above command
• [x] All new and existing tests passed. No? -> figure out why and add the fix to your commit. It is your responsibility to make sure your code works.
• [x] My pull request is based on the latest changes of the master branch. No? Unsure? -> execute command git pull --rebase upstream master

[ManojLL]

@isaacmujuni have you had a chance to go through this? https://openmrs.atlassian.net/wiki/spaces/docs/pages/25477199/Pull+Request+Tips ?