feat(consensus): add loopback queue for primary self-addressed messages

[hubcio]

The primary was sending PrepareOk to itself through the message
bus, requiring a network round-trip and an unwrap() on bus
errors. Replace with an in-process VecDeque that the simulator
drains after each dispatch. Cleared on view change reset and
on DVC quorum completion.

Includes defensive debug_assert guards on push_loopback
overflow, process_loopback buf precondition, and simulator
drain idempotency. Adds test verifying loopback is cleared
when complete_view_change_as_primary fires.

[codecov]

Codecov Report

❌ Patch coverage is 73.79913% with 60 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.86%. Comparing base (4f1044d) to head (b41e202).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
core/shard/src/lib.rs	0.00%	36 Missing ⚠️
core/consensus/src/plane_helpers.rs	88.41%	19 Missing ⚠️
core/simulator/src/lib.rs	0.00%	4 Missing ⚠️
core/consensus/src/impls.rs	96.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2825      +/-   ##
============================================
+ Coverage     67.55%   67.86%   +0.31%     
  Complexity      739      739              
============================================
  Files          1049     1049              
  Lines         84169    84385     +216     
  Branches      60746    60972     +226     
============================================
+ Hits          56859    57271     +412     
+ Misses        24958    24736     -222     
- Partials       2352     2378      +26     

Flag	Coverage Δ
csharp	67.43% <ø> (-0.19%)	⬇️
go	6.33% <ø> (ø)
java	54.83% <ø> (ø)
node	92.18% <ø> (-0.15%)	⬇️
python	0.00% <ø> (ø)
rust	70.18% <73.79%> (+0.47%)	⬆️

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

Files with missing lines	Coverage Δ
core/consensus/src/impls.rs	42.48% <96.00%> (+27.09%)	⬆️
core/simulator/src/lib.rs	0.00% <0.00%> (ø)
core/consensus/src/plane_helpers.rs	57.60% <88.41%> (+37.03%)	⬆️
core/shard/src/lib.rs	0.00% <0.00%> (ø)

... and 22 files with indirect coverage changes

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