Emit telemetry spans for move_in_query snapshot operations

[robacourt]

Summary

shape_snapshot.execute_for_shape and shape_snapshot.query_fn spans were missing from production traces for move_in_query operations, while initial_snapshot and subset_query worked fine. This wires up a parent span so the existing child spans get emitted.

Problem

Sampling for shape_snapshot.query_fn is a plain included?(_) -> true (no rate limiting), so the absence of move_in_query spans wasn't a sampling issue — the spans were never being created.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.82%. Comparing base (7f8947a) to head (5f6e9eb).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4303      +/-   ##
==========================================
+ Coverage   54.09%   58.82%   +4.72%     
==========================================
  Files         206      251      +45     
  Lines       20775    24468    +3693     
  Branches     5493     6376     +883     
==========================================
+ Hits        11239    14394    +3155     
- Misses       9532    10067     +535     
- Partials        4        7       +3     

Flag	Coverage Δ
packages/agents	67.80% <ø> (ø)
packages/agents-mcp	77.19% <ø> (?)
packages/agents-runtime	80.10% <ø> (ø)
packages/agents-server	69.19% <ø> (-0.08%)	⬇️
packages/agents-server-ui	5.31% <ø> (ø)
packages/electric-ax	38.04% <ø> (ø)
packages/experimental	87.73% <ø> (?)
packages/react-hooks	86.48% <ø> (?)
packages/start	82.83% <ø> (?)
packages/typescript-client	94.32% <ø> (?)
packages/y-electric	56.05% <ø> (?)
typescript	58.82% <ø> (+4.72%)	⬆️
unit-tests	58.82% <ø> (+4.72%)	⬆️

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