Compiler options should be possible to be set with `-D` without pom.xml `-A` mapping

[AndreasIgel]

Summary

All simple-builders compiler options (e.g. skipFormatting, generateJavaDoc, builderAccess, verbose) require a corresponding -Asimplebuilder.<option>=${simplebuilder.<option>} entry in the project's pom.xml <compilerArgs> section to reach the annotation processor. Setting -Dsimplebuilder.<option>=<value> on the Maven command line alone has no effect, because the annotation processor reads from processingEnv.getOptions() (which only receives -A prefixed args), not from JVM system properties.

The documentation at docs/CONFIGURATION.md and docs/DEBUG_LOGGING.md suggests that mvn compile -Dsimplebuilder.skipFormatting=true works, but this is only true for projects that already have the matching -A mapping in their pom.xml. Users who follow the documentation without adding the mapping will find the option silently ignored.

Steps to reproduce

1. In any project using simple-builders, run:

   mvn clean compile -Dsimplebuilder.generateJavaDoc=DISABLED

2. Check the generated builder source — javadoc is still present, the option had no effect.

Expected behaviour

-Dsimplebuilder.<option>=<value> on the command line should work without requiring additional pom.xml configuration, so users can easily test and toggle options from the console.

Proposed solution

Add a System.getProperty() fallback in CompilerArgumentsReader.readValue() so that JVM system properties (-D) are checked when the -A compiler arg is not present:

public String readValue(CompilerArgumentsEnum argument) {
    // 1. Try -A compiler arg (highest priority)
    String value = processingEnv.getOptions().get(argument.getCompilerArgument());
    if (value == null) {
        value = processingEnv.getOptions().get(argument.getOptionName());
    }
    // 2. Fallback: check JVM system property (-D on command line)
    if (value == null) {
        value = System.getProperty(argument.getCompilerArgument());
    }
    return value;
}

This establishes a clear priority chain:

1. Annotation values (@SimpleBuilder.Options) — highest priority
2. -A compiler args — medium priority (explicit, pom-configured)
3. -D system properties — fallback (command-line convenience)
4. Defaults — lowest priority

The -A path remains the canonical mechanism (as documented for Maven/Gradle/IntelliJ), while -D becomes a zero-config convenience for command-line usage.

Affected files

• processor/src/main/java/org/javahelpers/simple/builders/processor/processing/CompilerArgumentsReader.java — add system property fallback
• docs/CONFIGURATION.md — clarify that -D works as a fallback (no pom.xml change required)
• docs/DEBUG_LOGGING.md — already documents the -A requirement; update to mention -D also works

Impact

• No breaking changes — existing -A mappings continue to take priority
• Improved UX — all options work from command line out of the box
• Documentation becomes accurate — mvn compile -Dsimplebuilder.skipFormatting=true works as documented