[FLINK-35230][table] Split FlinkSqlParserImplTest into smaller test classes

[Au-Miner]

What is the purpose of the change

Split the monolithic FlinkSqlParserImplTest (4000+ lines) into smaller, focused test classes to improve maintainability and eliminate the Checkstyle FileLength suppression.

Brief change log

• Extract FlinkSqlParserTestBase as a shared base class providing fixture(), sql(), expr(), validated() methods
• Split into 10 domain-specific parser test classes: CatalogTest, MetadataTest, CreateTableTest, AlterTableTest, CtasTest, ViewTest, ModelTest, ConnectionTest, ExecuteTest, MiscTest
• Add FlinkSqlParserCalciteTest extending SqlParserTest to restore Calcite standard SQL test coverage (472 inherited tests)
• Consolidate 10 UnParser test files into a single FlinkSqlParserUnParserTest using JUnit 5 @Nested inner classes
• Remove FlinkSqlParserImplTest FileLength suppression from suppressions.xml

Verifying this change

This is a pure refactoring — 248 Flink-specific test methods before and after, verified via diff on extracted method names. The 472 inherited Calcite tests are now covered by FlinkSqlParserCalciteTest.

Does this pull request potentially affect one of the following parts

• Dependencies: no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Currentpoints, Savepoints: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• bae1270 Azure: SUCCESS

Bot commands

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• @flinkbot run azure re-run the last Azure build

[raminqaf]

LGTM!