fix(shard): tell an unknown consensus operation from a corrupt header

[numinnex]

Fixes given_an_unknown_operation_when_a_consensus_frame_decodes_should_surface_an_upgrade_fence_signal test.

[codecov]

Codecov Report

❌ Patch coverage is 90.74074% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.69%. Comparing base (c0c7493) to head (aa50652).

Files with missing lines	Patch %	Lines
core/shard/src/router.rs	62.50%	3 Missing ⚠️
core/server_common/src/consensus_message.rs	85.71%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3931      +/-   ##
============================================
- Coverage     83.87%   83.69%   -0.19%     
  Complexity     1358     1358              
============================================
  Files          1212     1212              
  Lines        166843   166601     -242     
  Branches     134306   134189     -117     
============================================
- Hits         139937   139432     -505     
- Misses        23266    23392     +126     
- Partials       3640     3777     +137     

Components	Coverage Δ
Rust Core	84.51% <90.74%> (-0.14%)	⬇️
Java SDK	66.67% <ø> (ø)
C# SDK	74.99% <ø> (-1.56%)	⬇️
Python SDK	90.13% <ø> (ø)
PHP SDK	84.48% <ø> (ø)
Node SDK	95.94% <ø> (+0.09%)	⬆️
Go SDK	68.32% <ø> (ø)

Files with missing lines	Coverage Δ
core/binary_protocol/src/consensus/header.rs	81.56% <ø> (ø)
core/binary_protocol/src/consensus/operation.rs	97.54% <100.00%> (+0.06%)	⬆️
core/server/src/partition_reconciler.rs	97.80% <100.00%> (+0.03%)	⬆️
core/shard/src/metrics.rs	86.55% <ø> (ø)
core/server_common/src/consensus_message.rs	81.80% <85.71%> (+0.50%)	⬆️
core/shard/src/router.rs	79.71% <62.50%> (+7.01%)	⬆️

... and 72 files with indirect coverage changes

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