[CELEBORN-2423] Fix rack-aware replica storage selection

[Kalvin2077]

What changes were proposed in this pull request?

This follow-up to PR #3781:

• Validates that rack-aware replica candidates support the requested storage type.
• Builds replica StorageInfo from the selected replica worker.
• Adds regression tests for diskless replicas and different mount points.

Why are the changes needed?

During best-effort fallback, the allocator could select a diskless worker for a local-disk replica or incorrectly reuse the primary worker's mount point.

Does this PR resolve a correctness bug?

• Yes

Does this PR introduce any user-facing change?

• Yes

How was this patch tested?

build/mvn -pl master -am -Dtest=SlotsAllocatorRackAwareSuiteJ test

[Kalvin2077]

@zaynt4606 @SteNicholas
PTAL, thx.

[yew1eb]

@Kalvin2077 LGTM overall. One nit on test coverage: offerSlotsRackAwareFallbackRequiresReplicaDisk only covers the case where no eligible replica exists. Could we add a case where the replica rack has both a diskless and a local-disk worker, and assert the allocator skips the diskless on and still allocates? That's the path the new canAssign predicate actually guards — currently it would regress unnoticed.