refactor(meta): separate validation and execution logic in alter logical tables procedure

[WenyXu]

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Refer to a related PR or issue link (optional)

#6429

What's changed and what's your intention?

This PR refactors the AlterLogicalTablesProcedure by separating validation and execution concerns into dedicated components.

Changes

• Add AlterLogicalTableValidator:

  • Validates schema consistency across alter expressions
  • Validates alter operation types (currently supports AddColumns)
  • Validates physical table existence and logical table relationships
  • Performs pre-execution checks

• New AlterLogicalTablesExecutor:

  • Handles metadata updates for alter operations
  • Manages region request generation and processing
  • Coordinates cache invalidation
  • Encapsulates all execution-related logic

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[fengjiachun]

Rest LGTM

[MichaelScofield]

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