Stabilize client network error coverage

[e-desouza]

Summary

• add typed client network error categories for async JSON-RPC/WebSocket clients
• map transport errors into XRPLNetworkErrorKind
• add integration-covered tests for exception mapping branches
• stabilize local standalone fee CLI coverage and update Codecov action to v5.5.5

Local validation

• cargo fmt --all -- --check
• cargo clippy --all-features -- -D warnings
• build matrix from Build & Lint workflow
• cargo test --release
• cargo test --release --no-default-features --features embassy-rt,core,utils,wallet,models,helpers,websocket,json-rpc
• unit cargo-llvm-cov thresholds
• integration cargo-llvm-cov against local xrpld via podman
• clio smoke: cargo run ... server fee --url http://localhost:51233

Integration patch coverage locally: 85.11%.

[codecov]

Codecov Report

❌ Patch coverage is 85.10638% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.52%. Comparing base (bbaef35) to head (6e9d2d3).

Files with missing lines	Patch %	Lines
src/asynch/clients/json_rpc/exceptions.rs	72.72%	3 Missing ⚠️
src/asynch/clients/websocket/exceptions.rs	88.00%	3 Missing ⚠️
src/asynch/clients/exceptions.rs	90.90%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #327   +/-   ##
=======================================
  Coverage   83.51%   83.52%           
=======================================
  Files         219      221    +2     
  Lines       22304    22351   +47     
=======================================
+ Hits        18628    18668   +40     
- Misses       3676     3683    +7     

Flag	Coverage Δ
integration	71.44% <85.10%> (+0.39%)	⬆️
unit	84.29% <ø> (ø)

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

Files with missing lines	Coverage Δ
src/asynch/clients/exceptions.rs	43.47% <90.90%> (+43.47%)	⬆️
src/asynch/clients/json_rpc/exceptions.rs	72.72% <72.72%> (ø)
src/asynch/clients/websocket/exceptions.rs	88.00% <88.00%> (ø)

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