Add StorageUnitConfiguration to encapsulate DataSourcePoolProperties

[menghaoranss]

Fixes #ISSUSE_ID.

Changes proposed in this pull request:

• Add StorageUnitConfiguration to encapsulate DataSourcePoolProperties

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[menghaoranss]

### Correction

- **Previous Finding:** Replacing the `DataSourceGeneratedDatabaseConfiguration` constructor could break external source or binary callers.
- **Current Status:** Withdrawn
- **Reason:** All repository references have been migrated to `StorageUnitConfiguration`. The class is under the internal `infra.config.database.impl` package, and the public evidence found only project-owned callers and the generated [ShardingSphere source xref](https://shardingsphere.apache.org/statistics/staging/shardingsphere-infra/shardingsphere-infra-common/xref/org/apache/shardingsphere/infra/config/database/impl/DataSourceGeneratedDatabaseConfiguration.html). There is no attributable external caller or documented supported-API contract. Therefore, the previous compatibility concern does not pass the blocker proof gate.

### Summary

**Review Result: Mergeable**

**Reason:** The latest code scope correctly introduces `StorageUnitConfiguration`, propagates it through YAML persistence, registry recovery, and Proxy database configuration, while preserving the existing metadata YAML structure and global data-source behavior. No code-level blocker remains. This result is code-scope only; CI was not reviewed by request.

### Evidence

- All repository constructor references use `Map<String, StorageUnitConfiguration>`.
- Existing `DatabaseConfiguration` implementations remain compatible through the default conversion method.
- Legacy metadata YAML is parsed through the existing `DataSourcePoolProperties` conversion path.
- New persistence still emits the existing data-source YAML structure.
- Proxy database data sources use the new configuration model; Proxy global data sources retain their previous path.
- Empty active-version and empty-version-content behavior remains covered.
- The latest-head focused test run passed 63 tests with no failures.

### Review Details

- **Review Focus:** Code Correctness Review. CI not reviewed by request.
- **Reviewed Scope:** All 20 changed files at head `a3a9c739584d364f4b79956ee98aa2507759a01e`; base and merge-base `43829a8d089cc4405b0177d1fee96f56293f6b94`. The local triple-dot file list matched GitHub `/pulls/39234/files`.
- **Not Reviewed Scope:** GitHub Actions, check runs, workflow logs, and external deployment environments.
- **Verification:** Spotless and Checkstyle passed. Focused tests across `infra/common`, `mode/core`, Cluster mode, Proxy backend, and CDC passed: 63 tests, 0 failures. The challenged compatibility premise was rechecked against all repository references and available public evidence.
- **Release Note / User Docs:** Not required. The persisted YAML format and user-facing Proxy configuration schema remain unchanged.