refactor(shard): drop journal generic, metrics scrape, poll cursor

[numinnex]

No description provided.

[numinnex]

merge after #3911

[codecov]

Codecov Report

❌ Patch coverage is 98.06630% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.65%. Comparing base (3db955e) to head (29fb52e).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
core/partitions/src/iggy_index_reader.rs	91.66%	0 Missing and 4 partials ⚠️
core/partitions/src/poll_plan.rs	98.79%	1 Missing ⚠️
core/server/src/dispatch.rs	97.67%	1 Missing ⚠️
core/shard/src/lib.rs	98.14%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3914       +/-   ##
=============================================
- Coverage     83.78%   67.65%   -16.14%     
  Complexity     1358     1358               
=============================================
  Files          1212     1211        -1     
  Lines        166189   146088    -20101     
  Branches     133663   113687    -19976     
=============================================
- Hits         139243    98834    -40409     
- Misses        23320    43554    +20234     
- Partials       3626     3700       +74     

Components	Coverage Δ
Rust Core	63.68% <96.74%> (-20.86%)	⬇️
Java SDK	66.67% <ø> (ø)
C# SDK	75.06% <ø> (-1.49%)	⬇️
Python SDK	90.00% <ø> (ø)
PHP SDK	84.48% <ø> (ø)
Node SDK	95.94% <ø> (ø)
Go SDK	68.32% <ø> (ø)

Files with missing lines	Coverage Δ
core/journal/src/lib.rs	25.00% <ø> (ø)
core/journal/src/prepare_journal.rs	90.44% <ø> (+0.08%)	⬆️
core/metadata/src/impls/metadata.rs	86.53% <ø> (-0.12%)	⬇️
core/partitions/src/iggy_partition.rs	87.29% <ø> (+0.41%)	⬆️
core/partitions/src/journal.rs	89.39% <ø> (ø)
core/partitions/src/log.rs	80.92% <100.00%> (ø)
core/server/src/auth.rs	90.12% <100.00%> (ø)
core/server/src/bootstrap.rs	80.79% <100.00%> (-0.03%)	⬇️
core/server/src/consumer_group.rs	97.29% <100.00%> (ø)
core/server/src/dispatch/authz.rs	94.77% <100.00%> (ø)
... and 11 more

... and 339 files with indirect coverage changes

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