[Fix](ai_agg) isolate AI_AGG query_ctx per aggregate state

[linrrzqqq]

Problem Summary:

AI_AGG previously stored QueryContext in a process-level static pointer. Concurrent AI_AGG queries could overwrite that pointer, causing one query to read another query's AI resource metadata, query options, or timeout state.

The aggregate function instance now receives the query context from AggFnEvaluator and binds it to each AggregateFunctionAIAggData state when the state is created, reset, or deserialized.

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[linrrzqqq]

/review

[github-actions]

Review result: no blocking issues found in this PR.

Critical checkpoint conclusions:

• Goal and proof: The PR removes the process-wide static QueryContext from AI_AGG and binds the context through AggregateFunctionAIAgg into each AggregateFunctionAIAggData state on create, reset, and deserialize. The added unit test covers two aggregate function instances with different context-window settings and verifies isolation.
• Scope and clarity: The modification is small and focused on the AI_AGG context lifetime issue.
• Concurrency: The removed static pointer was the shared mutable state. The replacement stores context on each aggregate function instance and copies it into each aggregate state; no new shared mutable state or lock ordering concern was introduced.
• Lifecycle: Aggregate states are initialized through create, reset, and deserialize before use. QueryContext is an observer pointer consistent with the existing RuntimeState/query lifecycle used by AggFnEvaluator.
• Configuration: No new configuration items are added.
• Compatibility: No storage format, thrift protocol, or function signature compatibility change is introduced.
• Parallel paths: Nullable aggregate wrappers delegate set_query_context to the nested function, and the aggregate create/deserialize/reset paths reviewed all preserve context propagation.
• Conditional checks: Existing context checks remain unchanged; no new speculative defensive checks were added.
• Test coverage: The new BE unit test directly exercises the fixed cross-instance isolation behavior. I did not run tests in this review environment.
• Observability: No new observability is required for this narrowly scoped lifecycle fix.
• Transaction/persistence/data writes: Not applicable.
• FE/BE variable passing: No new transmitted variables are added.
• Performance: No meaningful overhead beyond assigning a pointer during aggregate state lifecycle operations.

User focus response: No additional user-provided focus points were supplied, and no extra issue was found while reviewing the whole PR.

[linrrzqqq]

run buildall

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100.00% (12/12) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	74.38% (27999/37643)
Line Coverage	58.44% (304841/521663)
Region Coverage	56.12% (256308/456715)
Branch Coverage	57.57% (110649/192189)

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100.00% (12/12) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	73.76% (27764/37643)
Line Coverage	57.61% (300523/521663)
Region Coverage	54.78% (250184/456715)
Branch Coverage	56.36% (108314/192189)

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100.00% (12/12) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	73.76% (27764/37643)
Line Coverage	57.60% (300460/521663)
Region Coverage	54.79% (250225/456715)
Branch Coverage	56.34% (108283/192189)