refactor(configs): move ServerConfig types from server to configs crate

[hubcio]

Config types were coupled to the server binary, forcing
dependents to pull in the entire server crate. Move them
to core/configs/ with a thin re-export facade so existing
server imports stay unchanged.

Add TODO for extracting iggy_types leaf crate to break
the configs <-> iggy_common cycle and eliminate the
MemoryPoolConfigOther duplicate.

[codecov]

Codecov Report

❌ Patch coverage is 34.60490% with 240 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.40%. Comparing base (f36c5ee) to head (87cb236).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
core/server/src/shard_allocator.rs	13.44%	203 Missing and 3 partials ⚠️
core/configs/src/server_config/sharding.rs	74.01%	24 Missing and 9 partials ⚠️
core/configs/src/server_config/validators.rs	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (34.60%) is below the target coverage (50.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2796   +/-   ##
=========================================
  Coverage     68.39%   68.40%           
  Complexity      656      656           
=========================================
  Files           852      853    +1     
  Lines         68185    68176    -9     
  Branches      59646    59647    +1     
=========================================
- Hits          46636    46634    -2     
+ Misses        19212    19198   -14     
- Partials       2337     2344    +7     

Flag	Coverage Δ
csharp	67.06% <ø> (-0.19%)	⬇️
java	52.19% <ø> (ø)
rust	69.58% <34.60%> (+0.02%)	⬆️

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

Files with missing lines	Coverage Δ
core/common/src/alloc/memory_pool.rs	70.30% <ø> (ø)
core/configs/src/server_config/cache_indexes.rs	27.58% <ø> (ø)
core/configs/src/server_config/defaults.rs	0.00% <ø> (ø)
core/configs/src/server_config/displays.rs	93.04% <ø> (ø)
core/configs/src/server_config/http.rs	66.66% <ø> (ø)
core/configs/src/server_config/server.rs	66.66% <100.00%> (ø)
core/configs/src/server_config/system.rs	94.21% <ø> (ø)
core/configs/src/server_config/websocket.rs	14.70% <ø> (ø)
core/server/src/bootstrap.rs	80.68% <ø> (ø)
core/server/src/main.rs	66.13% <ø> (ø)
... and 4 more

... and 15 files with indirect coverage changes

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