[BugFix] Add TYPE_DECIMAL256 support for column aggregators in PRIMARY KEY tables

[stephen-shelby]

Why I'm doing:

When using DECIMAL columns with precision > 38 (e.g., DECIMAL(39,0)) in PRIMARY KEY tables, the backend crashes during data insertion:

Check failed: false unreachable path, unknown key column type: 26

The column aggregator factory doesn't support TYPE_DECIMAL256 (type ID 26), which is required for decimal precision between 39-76.

What I'm doing:

Backend fix (be/src/storage/column_aggregate_func.cpp):

• Add TYPE_DECIMAL256 support for REPLACE aggregation (line 380)
• Add TYPE_DECIMAL256 support for key column aggregation (line 427)

Fixes #67991

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
  • 3.4

[StarRocks-Reviewer]

@cursor review

[github-actions]

[Java-Extensions Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[BE Incremental Coverage Report]

❌ fail : 0 / 2 (00.00%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	be/src/storage/column_aggregate_func.cpp	0	2	00.00%	[380, 427]

[github-actions]

@Mergifyio backport branch-4.0

[github-actions]

@Mergifyio backport branch-4.1

[mergify]

backport branch-4.0

✅ Backports have been created

Details

• #68192 [BugFix] Add TYPE_DECIMAL256 support for column aggregators in PRIMARY KEY tables (backport #68134) has been created for branch branch-4.0

[mergify]

backport branch-4.1

✅ Backports have been created

Details

• #68193 [BugFix] Add TYPE_DECIMAL256 support for column aggregators in PRIMARY KEY tables (backport #68134) has been created for branch branch-4.1