[Refactor] Split schema scanners into layered modules

[alvin-phoenix-ai]

Why I'm doing:

What I'm doing:

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
  • This pr needs auto generate documentation
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.1
  • 4.0
  • 3.5

[CelerData-Reviewer]

@codex review

[github-actions]

Module-risk briefing for Codex review

This is review focus, not a finding list. Validate against the diff.

High-confidence risks

• Module: exec/schema_scanner
  Changed files: schema_column_filler.h, schema_helper.cpp/.h, schema_partitions_meta_scanner.cpp, schema_fe_metrics_scanner.cpp, schema_fe_tablet_schedules_scanner.cpp, schema_be_tablets_scanner.cpp, schema_be_txns_scanner.cpp, schema_be_compactions_scanner.cpp, schema_be_cloud_native_compactions_scanner.cpp, schema_be_datacache_metrics_scanner.cpp, schema_be_logs_scanner.cpp, schema_be_tablet_write_log_scanner.cpp
  Historical failure pattern: This module's fixes recur around fill_chunk column-type/behavior drift and scanner-startup wiring gaps, because scanner column layout and the FE↔BE contract have no single source of truth or compile-time cross-check.
  Review focus: (1) SchemaPartitionsMetaScanner::fill_chunk case 22 (DATA_SIZE) now calls the relocated ParseUtil::parse_data_size instead of the old free-function parse_data_size in storage/utils.cpp — diff against the byte-for-byte old body (isdigit/toupper now cast to unsigned char, overflow check changed from > max to >= 0x1p63) and confirm no behavior actually changed despite the PR being labeled "no behavior change". (2) fill_data_column_with_null moved from schema_helper.cpp into schema_column_filler.h as inline — check every scanner that used the old declaration still links/behaves identically (ODR/inline semantics). (3) The scanner-type→scanner switch was relocated verbatim from schema_scanner_factory.cpp into a new builtin_schema_scanner_factory.cpp behind a pluggable SchemaScannerFactory* reached via ExecEnv::schema_scanner_factory(); verify every TSchemaTableType case made the move intact (none dropped/reordered) and that every BE entry point that constructs ExecEnv/calls init() (not just starrocks_be.cpp) threads a real factory — create_schema_scanner() now hard-fails with InternalError instead of the old silent SchemaDummyScanner default when the factory is null, which is a new failure mode for every information_schema.* query if any startup path misses the wiring.
  Evidence: [BugFix] Populate DATETIME_PRECISION in information_schema.COLUMNS #74623, [BugFix] Push down table_name predicate for tables_config #73210, [BugFix] carry load times as UTC epoch ms across BE/FE thrift #73365, [BugFix] Be crash while query information_schema.warehouse_queries #72019, [BugFix] Add warehouse info to information_schema.task_runs and adjust scanner tests #70512, [BugFix] Support fetching tablet infos based on run mode in SchemaBeTabletsScanner #69645, [BugFix] Fix the bug of json parse in get fe metrics #68164, https://github.com/celerdata/celerdata-enterprise/pull/46246 (from 8 merged bugfixes)

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Remove the new ExecEnv include from exec scan code

be/src/exec/AGENTS.md:9 explicitly says not to add new production includes of exec/exec_env.h under be/src/exec; this new include (and the matching one added in pipeline/scan/schema_chunk_source.cpp) reintroduces ExecEnv coupling into schema scan execution just to fetch the factory, undercutting the layering this refactor is trying to enforce. Please route the factory through a lower-level scan context/interface instead of adding new ExecEnv dependencies here.

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