[fix][broker] Prevent BookkeeperSchemaStorage and BookkeeperBucketSnapshotStorage from bypassing namespace bookie affinity

[void-ptr974]

Motivation

When a namespace has a bookie affinity group, or strict bookie affinity selects the isolated placement policy, managed-ledger data uses the matching placement-aware BookKeeper client. BookkeeperSchemaStorage and BookkeeperBucketSnapshotStorage instead created their auxiliary ledgers with their independently configured default clients and did not persist the selected placement policy in ledger metadata.

As a result, newly created schema and delayed-delivery bucket ledgers could be placed outside the namespace's configured bookie groups. Bookie replacement for those ledgers also lacked the placement metadata needed to preserve the same policy.

Modifications

• Resolve the schema or delayed-bucket owner topic before creating a ledger.
• Borrow the placement-aware BookKeeper client introduced by [improve][broker] Add topic-aware BookKeeper context for auxiliary ledger placement #26702 and add the matching standard placement-policy metadata to the ledger.
• Recognize canonical schema storage keys, including encoded local names and scalable topic names.
• Preserve the existing default-client behavior for arbitrary and legacy schema storage keys that do not identify an unambiguous owner topic.
• Keep placement failures strict: do not silently fall back to the default client.
• Preserve delayed-bucket retry behavior by exposing policy lookup and client creation failures as BucketSnapshotPersistenceException.

Impact

• Only newly created schema and delayed-delivery bucket ledgers are affected; existing ledgers and their read/delete paths are unchanged.
• Namespaces without a custom or strict placement policy continue to use the shared default BookKeeper client and do not receive placement metadata.
• Placement clients are cached by policy configuration and borrowed from managed-ledger storage; this does not create one BookKeeper client per topic.
• Canonical three-part schema keys inherit the owner namespace policy. Arbitrary and legacy keys continue to use the schema storage's existing default client.

Stack

Depends on #26702. This branch contains the dependency commit; the commit specific to this PR is a7b2ccb439f.

Tests

• ./gradlew :pulsar-broker:test --no-build-cache --tests org.apache.pulsar.broker.service.schema.BookkeeperSchemaStorageTest --tests org.apache.pulsar.broker.service.schema.SchemaServiceTest --tests org.apache.pulsar.broker.delayed.BookkeeperBucketSnapshotStorageTest --tests org.apache.pulsar.broker.delayed.bucket.BookkeeperBucketSnapshotStoragePlacementTest
• ./gradlew :pulsar-broker:checkstyleMain :pulsar-broker:checkstyleTest

[void-ptr974]

Closing in favor of #26705. The schema and delayed-delivery bucket change remains the second of the three commits in that unified PR, whose description now documents the complete problem, implementation, and impact.