[cleanup](build) Replace #include exec_env.h with forward declaration in 15 headers

[shuke987]

Summary

• Remove unused #include "runtime/exec_env.h" from 7 header files where ExecEnv is not referenced at all
• Replace #include "runtime/exec_env.h" with class ExecEnv; forward declaration in 8 header files that only use ExecEnv* (pointer/reference)
• Move the full #include "runtime/exec_env.h" to corresponding .cpp files where needed to maintain compilation

This reduces the include fan-out of exec_env.h (591 lines) across the codebase, improving incremental build times when exec_env.h or any of its transitive dependencies change.

Headers with include removed (unused):

• pipeline/exec/aggregation_sink_operator.h
• vec/exec/scan/vscanner.h
• vec/sink/load_stream_map_pool.h
• vec/sink/load_stream_stub.h
• vec/sink/writer/vtablet_writer_v2.h
• vec/sink/writer/vtablet_writer.h
• olap/wal/wal_info.h

Headers with forward declaration added:

• agent/workload_sched_policy_listener.h
• runtime/group_commit_mgr.h
• olap/wal/wal_manager.h
• olap/wal/wal_table.h
• runtime/query_context.h
• runtime/workload_management/workload_sched_policy_mgr.h
• http/action/compaction_score_action.h
• http/http_handler_with_auth.h

Test plan

• Verify full build passes (run buildall)
• No functional changes - purely mechanical include cleanup
• Each header still compiles standalone (forward declarations provide the needed type info for pointer/reference usage)

🤖 Generated with Claude Code

[shuke987]

run buildall

[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?

[shuke987]

Closing: file paths were wrong. Will resubmit with verified changes.