test: e2e + unit coverage for ModifyInstanceAttribute and key service

- Add Phase 7b to single-node E2E: stop instance, modify type (nano →
  xlarge), start, SSH in, verify vCPU count (nproc) and memory
  (/proc/meminfo) match the new instance type
- Add Phase 8q negative test: modify-instance-attribute on running
  instance expects InvalidInstanceID.NotFound
- Improve key service integration test coverage (mulga-580)
- Pin viperblock/predastore CI checkout to main (fixes feature branch CI)
- Update TEST_COVERAGE.md

.github/workflows/hive.yml

@@ -29,14 +29,12 @@ jobs:
         uses: actions/checkout@v6
         with:
           repository: mulgadc/viperblock
-          ref: ${{ github.ref_name }}
           path: viperblock
 
       - name: Checkout Predastore
         uses: actions/checkout@v6
         with:
           repository: mulgadc/predastore
-          ref: ${{ github.ref_name }}
           path: predastore
 
       - name: Setup Go Workspace
@@ -71,14 +69,12 @@ jobs:
         uses: actions/checkout@v6
         with:
           repository: mulgadc/viperblock
-          ref: ${{ github.ref_name }}
           path: viperblock
 
       - name: Checkout Predastore
         uses: actions/checkout@v6
         with:
           repository: mulgadc/predastore
-          ref: ${{ github.ref_name }}
           path: predastore
 
       - name: Setup Go Workspace
@@ -107,14 +103,12 @@ jobs:
         uses: actions/checkout@v6
         with:
           repository: mulgadc/viperblock
-          ref: ${{ github.ref_name }}
           path: viperblock
 
       - name: Checkout Predastore
         uses: actions/checkout@v6
         with:
           repository: mulgadc/predastore
-          ref: ${{ github.ref_name }}
           path: predastore
 
       - name: Setup Go Workspace