Build: Replace deprecated Groovy space-assignment property syntax in build scripts

[wombatu-kun]

Closes #15976

Summary

Gradle deprecated the Groovy DSL "space-assignment" syntax for setting properties (e.g. exceptionFormat "full") in favor of explicit assignment (exceptionFormat = "full"). It currently emits Properties should be assigned using the 'propName = value' syntax … warnings and is scheduled for removal in Gradle 10. This migrates the remaining space-assignment usages across the build scripts so the build is quiet under --warning-mode all and ready for the eventual Gradle upgrade — the repository was already mostly migrated, and this completes it.

Issue: #15976

What changed

Converted every remaining space-assignment property setter to name = value (22 occurrences across 13 build scripts), preserving the existing quote style:

• exceptionFormat = "full" and maxHeapSize = '…' in test / test-logging config (build.gradle, mr/build.gradle, spark/v3.5|v4.0|v4.1/build.gradle).
• zip64 = true in every shadowJar { } block (build.gradle ×2, the aws-/azure-/gcp-bundle builds, and the Spark and Flink runtime bundles).
• group = 'build' on the sourceJar/javadocJar tasks and username =/password = in the Maven credentials { } block (deploy.gradle).
• destinationDir = … on the aggregateJavadoc task (tasks.gradle).

Genuine method calls that merely resemble the pattern were intentionally left unchanged — e.g. events "passed", "failed", systemProperty 'k', v, source javadocTasks.source, and configurations = [...] (already correct). Unrelated deprecation categories (e.g. JavaPluginConvention from plugins, reserved configuration names) are out of scope for this issue.

Tests

This is a build-script syntax migration with no runtime behavior change, so no unit tests apply. Verified by ./gradlew help --warning-mode all -DallModules=true — configures every Spark/Flink/Kafka/Scala module with BUILD SUCCESSFUL and zero propName = value warnings remaining (a clean configure also proves each conversion targets a real settable property) — and by ./gradlew :iceberg-core:test --tests "org.apache.iceberg.TestTableMetadata.testJsonConversion" --warning-mode all, confirming the converted test/testLogging config still runs at execution time.