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 41.71429% with 204 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.48%. Comparing base (514b5c5) to head (1cf4dd7).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
core/server/src/shard_allocator.rs	15.45%	172 Missing and 3 partials ⚠️
core/configs/src/server_config/sharding.rs	82.48%	14 Missing and 10 partials ⚠️
core/configs/src/server_config/validators.rs	0.00%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2796      +/-   ##
============================================
+ Coverage     71.44%   71.48%   +0.04%     
  Complexity      708      708              
============================================
  Files           969      970       +1     
  Lines         78219    78195      -24     
  Branches      60029    60013      -16     
============================================
+ Hits          55884    55901      +17     
+ Misses        20002    19949      -53     
- Partials       2333     2345      +12     

Flag	Coverage Δ
csharp	67.06% <ø> (-0.19%)	⬇️
java	54.02% <ø> (ø)
node	92.18% <ø> (-0.23%)	⬇️
rust	69.64% <41.71%> (+0.08%)	⬆️

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 14 files with indirect coverage changes

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