[cueadmin] Add Unit Tests for Subscription Management (AcademySoftwareFoundation#1984)

**Link the Issue(s) this Pull Request is related to.**
- AcademySoftwareFoundation#1920 

**Summarize your change.**

Implement tests for subscription commands that manage show-allocation
relationships and resource allocation.

Create `cueadmin/tests/test_subscription_commands.py` testing:
- -lb listing subscriptions for shows
- -lba listing all subscriptions to an allocation
- -create-sub creating new subscriptions with size/burst values
- -delete-sub removing subscriptions
- -size and -burst modifying subscription parameters
- Subscription query filtering
- Validation of size/burst values (non-negative, within limits)

Test various subscription configurations and verify resource calculation
accuracy.

Co-authored-by: Ramon Figueiredo <rfigueiredo@imageworks.com>
Co-authored-by: Aniket Singh Yadav <singhyadavaniket43@gmail.com>

Author: Aniketsy