Preserve DataFusion benchmark defaults

[gabotechs]

Summary

• make DataFusion session-setting CLI options optional
• emit each SET statement only when its corresponding flag was explicitly provided
• preserve explicit false and zero values

This lets benchmark subjects use their own defaults unless the benchmark invocation intentionally overrides them.

Validation

• npm run build
• npm test (106 tests)
• npm --prefix benchmarks-remote run application:build
• verified CLI help no longer advertises defaults for these flags
• git diff --check