Fix editable/debug build after StructVector API change and vector header split

[aaron-ang]

Summary

Three small fixes to make the editable / debug build (the one configured with DISABLE_UNITY = "1" in pyproject.toml, used when running the steps in CLAUDE.md) work end-to-end:

1. StructVector::GetEntries now returns vector<Vector> & instead of vector<unique_ptr<Vector>> & — duckdb/duckdb@4e5d5da6a6 "Make StructVector have the same layout as DataChunk (vector)". The two call sites in this repo still iterate via *children[i], which becomes a type error (no match for 'operator*' (operand type is 'duckdb::Vector')).
2. ListVector / ArrayVector / StructVector / MapVector were moved into their own headers under duckdb/common/vector/. With unity disabled they are no longer pulled in transitively, so building fails with 'ListVector' has not been declared / 'ArrayVector' has not been declared / 'StructVector' has not been declared / 'MapVector' has not been declared (and follow-on 'VALID' / 'DUPLICATE_KEY' is not a member of 'duckdb::MapInvalidReason').
3. .clangd points at build/clangd/, but the editable build writes compile_commands.json to build/debug/ (per the build-dir override in pyproject.toml). Result: clangd has no compile DB to read and reports 'file not found' on every project header in any IDE that uses clangd (VS Code, CLion, etc.).

cibuildwheel (CI release path) uses the default unity-enabled Release config and does not exercise issues 1 or 2, which is why this regression went unnoticed. Issue 3 is silent at build time and only shows up in the IDE.

Changes

• Drop the deref in *struct_children[i] / *children[i] at the two StructVector::GetEntries call sites.
• Add explicit #include for the four vector headers in the three files that reference those types.
• Repoint .clangd CompilationDatabase from build/clangd to build/debug so it matches the actual editable build directory.

Test plan

• Followed CLAUDE.md two-step editable build on a fresh .venv (uv sync --only-group build --no-install-project -p 3.13 → uv sync --no-build-isolation -v --reinstall -p 3.13). Build now succeeds.
• .venv/bin/pytest tests/fast/spark/ against the resulting debug install: 300 passed, 4 skipped, 1 xfailed, 0 failures.
• After the .clangd change, opening any project .cpp file in VS Code with the clangd extension resolves all duckdb/... and duckdb_python/... includes without a manual symlink.

Related

Pairs with duckdb/duckdb#22551 — a parallel upstream fix for ~15 missing create_*_info.hpp includes inside the submodule that also break debug builds (dynamic_cast to forward-declared types in D_ASSERT). This PR fixes the package-side issues; duckdb/duckdb#22551 fixes the engine-side issues. Once duckdb/duckdb#22551 lands and the submodule pin is bumped, this PR completes the debug-build fix on its own.