feat: add spill-backed sorting and aggregation

[KKould]

What problem does this PR solve?

Sort and aggregation currently need to keep their working rows in memory, and equi-join implementation selection always prefers HashJoin. This makes large ORDER BY, GROUP BY, and DISTINCT workloads more memory-sensitive, and leaves no SQL-level escape hatch for forcing a bounded-memory aggregate or nested-loop join plan.

Issue link: N/A

What is changed and how it works?

• Adds an optional spill feature with a spill-file backed SpillVec and codec support for temporary executor rows.
• Uses a spill-backed ExternalSort when the spill feature is enabled, including sorted segments and merge passes.
• Adds StreamAggregate and generalizes ordered-input optimization so DISTINCT and grouped aggregation can reuse existing ordering.
• Adds the FORCE_AGG_SPILL optimizer hint, routing grouped aggregates and distinct aggregates through ordered stream execution and inserting a Sort only when the input is not already ordered.
• Adds the FORCE_NEST_LOOP_JOIN optimizer hint to override equi-join HashJoin selection when needed.
• Documents the spill feature and optimizer hints, and enables spill coverage in sqllogictest.

Code changes

• Has Rust code change
• Has CI related scripts change

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

The coverage includes SpillVec and codec behavior, external sort segment/merge correctness, stream aggregate and distinct planning/results, forced aggregate spill planning/results, and forced nested-loop join Explain coverage.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Note for reviewer

The spill-backed sort path is gated by the spill feature and remains unavailable for wasm. FORCE_AGG_SPILL first reuses existing ordered input when possible, so it only adds an explicit Sort for unordered aggregate inputs.

[codecov]

Codecov Report

❌ Patch coverage is 96.64879% with 50 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.91%. Comparing base (3f0df6f) to head (506bd78).

Files with missing lines	Patch %	Lines
src/execution/dql/external_sort.rs	96.17%	12 Missing ⚠️
src/optimizer/rule/normalization/elimination.rs	92.48%	10 Missing ⚠️
src/binder/parser.rs	90.41%	7 Missing ⚠️
src/execution/spill/mod.rs	98.75%	6 Missing ⚠️
src/execution/dql/aggregate/mod.rs	84.37%	5 Missing ⚠️
src/execution/dql/aggregate/stream_agg.rs	98.00%	3 Missing ⚠️
src/orm/mod.rs	76.92%	3 Missing ⚠️
src/parser/mod.rs	77.77%	2 Missing ⚠️
src/execution/dql/sort.rs	98.00%	1 Missing ⚠️
src/optimizer/rule/implementation/dql/join.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #377      +/-   ##
==========================================
+ Coverage   92.85%   92.91%   +0.05%     
==========================================
  Files         249      253       +4     
  Lines       41844    43141    +1297     
==========================================
+ Hits        38856    40084    +1228     
- Misses       2988     3057      +69     

Flag	Coverage Δ
rust	92.91% <96.64%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/binder/aggregate.rs	97.48% <100.00%> (+<0.01%)	⬆️
src/binder/distinct.rs	98.48% <100.00%> (+0.01%)	⬆️
src/binder/mod.rs	85.58% <100.00%> (+0.06%)	⬆️
src/binder/select.rs	94.31% <100.00%> (+0.01%)	⬆️
src/db.rs	92.96% <ø> (+0.05%)	⬆️
src/errors.rs	98.55% <ø> (ø)
src/execution/dql/aggregate/hash_agg.rs	98.42% <100.00%> (+3.06%)	⬆️
src/execution/dql/aggregate/stream_distinct.rs	97.54% <100.00%> (+0.03%)	⬆️
src/execution/dql/join/hash_join.rs	97.05% <100.00%> (+0.02%)	⬆️
src/execution/dql/join/nested_loop_join.rs	97.90% <100.00%> (-0.32%)	⬇️
... and 27 more

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