[Feature][Common] Migrate conf package from Scala to Java

[och5351]

What this PR does

Converts 9 Scala files in streampark-common/src/main/scala/org/apache/streampark/common/conf/ to pure Java as part of the Scala removal plan (#4408).

Converted files

Scala	Java
ConfigKeys.scala	ConfigKeys.java
InternalOption.scala	InternalOption.java
InternalConfigHolder.scala	InternalConfigHolder.java
CommonConfig.scala	CommonConfig.java
K8sFlinkConfig.scala	K8sFlinkConfig.java
ConfigOption.scala	ConfigOption.java
Workspace.scala	Workspace.java
FlinkVersion.scala	FlinkVersion.java
SparkVersion.scala	SparkVersion.java

Notable design decisions

• InternalOption<T>: Made generic (InternalOption<T>) to eliminate unchecked casts in InternalConfigHolder.get(InternalOption<T>). Each config constant exposes a static accessor method (e.g. CommonConfig.MAVEN_SETTINGS_PATH()) to preserve backward compatibility with existing Java callers that relied on Scala val compiling to a no-arg method.
• InternalOption accessors: Added both getKey()-style (Java convention) and key()-style (Scala case class compatible) accessors to support mixed callers during the migration period.
• ConfigOption: Scala implicit parameters (implicit prefix: String, implicit prop: Properties) converted to Builder pattern.
• Workspace: Scala lazy val fields converted to eagerly-initialized constructor fields with DCL (volatile) for singleton instances.
• FlinkVersion / SparkVersion: Scala lazy val fields compile to no-arg methods in bytecode, so accessor methods use the same names without get prefix (e.g. version(), scalaVersion()) to keep Scala callers working.

Scope extension — TypeCastUtils.java

TypeCastUtils.java is added to the util package as a replacement for Implicits.cast[T], a Scala extension method that Java code cannot call. Three of the converted files require string-to-type casting. Implicits.scala (and its cast method) will be removed when all remaining Scala files are converted.

Also updated

• EnvInitializer.java in streampark-console-service: updated raw InternalOption reference to InternalOption<?> following the generic change.

Testing

• mvn compile -pl streampark-common passes
• mvn test -pl streampark-common passes (13 tests)

closes #4408 (partial — Phase 1.1)

[sonarqubecloud]

Quality Gate passed

Issues
100 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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