feat(sync-service): Support multiple subqueries at the same level

[robacourt]

Support multiple subqueries at the same level in shape where clauses (e.g., x IN (subquery) AND y IN (subquery)), addressing #3675.

Previously, shapes with multiple same-level subqueries were rejected with a 400 error. This PR removes that restriction and:

• Updates DependencyLayers to correctly layer shapes with multiple dependencies by placing them after all dependencies are found (1 + max layer of all dependencies)
• Fixes extract_subqueries to preserve AST traversal order
• Returns 409 (shape invalidation) on move-in/out operations for shapes with multiple same-level subqueries, since we cannot correctly determine which dependency caused the change

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.91%. Comparing base (393eca2) to head (413eebf).
⚠️ Report is 11 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3676   +/-   ##
=======================================
  Coverage   87.91%   87.91%           
=======================================
  Files          22       22           
  Lines        1820     1820           
  Branches      458      460    +2     
=======================================
  Hits         1600     1600           
  Misses        218      218           
  Partials        2        2           

Flag	Coverage Δ
packages/experimental	87.73% <ø> (ø)
packages/react-hooks	86.48% <ø> (ø)
packages/start	89.58% <ø> (ø)
packages/typescript-client	93.66% <ø> (ø)
packages/y-electric	56.05% <ø> (ø)
typescript	87.91% <ø> (ø)
unit-tests	87.91% <ø> (ø)

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