Echo cross attributes on execution reports

[pedrosakuma]

Summary

• echo crossType/crossPrioritization on cross-generated EntryPoint ExecutionReport_New and ExecutionReport_Trade frames
• thread cross attributes through non-persisted matching events for cross submit/sweep paths
• update GAP-30 compliance note and add encoder/core regression tests

Fixes #529

Validation

• dotnet restore SbeB3Exchange.slnx
• dotnet build SbeB3Exchange.slnx --no-restore -c Release
• dotnet test SbeB3Exchange.slnx --no-build -c Release
• dotnet test SbeB3Exchange.slnx -c Debug --filter "FullyQualifiedNameCrossOrder|FullyQualifiedNameExecutionReportEncoder"
• dotnet format SbeB3Exchange.slnx --verify-no-changes --no-restore --severity warn