[fix](balance) Fix PartitionRebalancer generating invalid moves to BEs without required storage medium (#62206)

[deardeng]

pick from #62206

When tablet_rebalancer_type=Partition, adding a new BE with only HDD disks to a cluster where tables use SSD storage medium causes the PartitionRebalancer to generate invalid moves (SSD tablets -> HDD-only BE), resulting in infinite "paths has no available balance slot: []" scheduling failures.

Root cause:

1. In LoadStatisticForTag.init(), beByTotalReplicaCount for each medium includes ALL available BEs without checking hasMedium(). This causes the greedy algorithm to consider HDD-only BEs as valid destinations for SSD tablets.
2. In LocalTabletInvertedIndex.buildPartitionInfoBySkew(), the countMap initialization uses all availableBeIds without medium filtering, so HDD-only BEs get counted with 0 replicas for SSD partitions, making them appear as the "least loaded" and preferred move target.

Fix:

1. Add hasMedium() filter in LoadStatisticForTag.init() when building beByTotalReplicaCount, so only BEs that actually have the required medium are considered for balancing.
2. Add availableBeIdsByMedium parameter to buildPartitionInfoBySkew() and use it to initialize countMap with only medium-matching BEs, preventing BEs without the required medium from appearing in the skew calculation.

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

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[hello-stephen]

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[deardeng]

run buildall