DBSIZE takes time in minutes and keyspace info missing when SSD storage tier is enabled

### Describe the bug

When running Garnet v1.0.87 with SSD storage tier enabled, the DBSIZE command becomes extremely slow (5-10 minutes) after loading data. Additionally, the INFO command does not show any keyspace section, even though keys exist in SSD tier.

- This issue is consistently reproducible.

### Steps to reproduce the bug

1. Start Garnet on a GCP C4D-HighMem-64 machine with the following configuration:
```
{
"Port": 6379,
"Address": "0.0.0.0",
"MemorySize": "16g",
"PageSize": "32m",
"SegmentSize": "4g",
"IndexSize": "16g",
"IndexMaxSize": "64g",
"IndexResizeFrequencySecs": 30,
"IndexResizeThreshold": 65,
"EnableReadCache": true,
"ReadCacheMemorySize": "420g",
"ReadCachePageSize": "2m",
"DisableObjects": true,
"EnableStorageTier": true,
"LogDir": "/mnt/localssd/garnet/log",
"CheckpointDir": "/mnt/localssd/garnet/ckpt",
"Recover": true,
"EnableAOF": false,
"CompactionFrequencySecs": 0,
"LogLevel": "Information",
"MetricsSamplingFrequency": 10
}
```
2. Load ~1.2 GB of data into the SSD tier using:
```
docker run --rm \
--cpus="$(nproc)" \
--memory="$(free -m | awk '/^Mem:/{print int($2*0.95)"m"}')" \
--network host \
redislabs/memtier_benchmark:latest \
-d 256000 \
--distinct-client-seed \
-h \
--ratio 1:0 \
--key-maximum 300000000 \
-c 15 -t "$(nproc)" \
--test-time 1000
```
3. After load is complete:
- Run DBSIZE → takes 5-10 minutes
- Run INFO → keyspace section is missing

### Expected behavior

- DBSIZE should return quickly without long blocking durations.
- INFO should display keyspace details even when keys are stored in SSD tier.

### Screenshots

### Release version

v1.0.87

### IDE

N/A (server-side issue)

### OS version

Ubuntu 24.04.3 LTS

### Additional context

_No response_

Start by reproducing the issue with the supplied Garnet configuration and benchmark, then run DBSIZE and INFO after the SSD-tier load completes. Trace the DBSIZE and INFO command paths alongside storage-tier key handling; done means DBSIZE returns without multi-minute blocking and INFO includes keyspace details for SSD-tier keys.

Written by the indexing model from the issue text.