Fix Iceberg column metadata for extended queries

[EDsCODE]

Summary

• Route extended/prepared SELECT execution through the existing Iceberg metadata pre-load helper.
• Keep simple SELECT behavior unchanged while sharing the metadata-aware query wrapper.
• Add regression coverage for metadata-loading and non-compat skip behavior.

Test Plan

• go test ./server -run 'TestQueryWithArgsWithMetadata|TestShouldLoadIcebergColumnMetadataOnlyForLakekeeper|TestLoadIcebergColumnMetadataUsesConnectionIcebergConfig' -count=1
• go test ./server -count=1
• just lint (blocked locally: golangci-lint not found)