feat: add Java writer and Gradle support, fix parser stability issues

[thunguo]

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feat

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en:

1. Add Java Writer

• Created lang/java/writer/write.go and lang/java/writer/ast.go, implementing a Java code generator (uniast.Writer interface) that supports generating Java source code and pom.xml from UniAST
• Created lang/java/writer/write_test.go with comprehensive unit tests
• Modified lang/write.go and lang/patch/lib.go to register the Java Writer into the framework

2. Add Gradle Project Support (Is there any plan to support java gradle project ? #146)

• Created lang/java/parser/gradle_parser.go, using regex to extract project structure from settings.gradle(.kts) / build.gradle(.kts) and outputting ModuleInfo in the same format as the Maven parser
• Created lang/java/parser/gradle_parser_test.go and testdata/java/5_gradle_project/ test data
• Modified NewJavaSpec in lang/java/spec.go: three-level detection — Maven → Gradle → empty fallback
• Modified lang/collect/collect.go: added Gradle fallback to both ScannerByTreeSitter and ScannerByJavaIPC

3. Fix Non-Deterministic Output (parser/java: output instability #95)

• lang/collect/export.go: receivers map entries are now sorted by source position after collection, ensuring stable method ordering
• lang/collect/collect.go: fallback file traversal changed to iterate over a sorted list, eliminating map random ordering

4. Fix FileImports Panic

• lang/java/spec.go: replaced panic("Java import parsing by tree-setting") with a regex-based import parsing implementation

5. Fix Writer Import Lookup Failure

• lang/java/writer/write.go: keys in mod.Files are relative paths — fixed by matching on basename instead

6. Improve extractPackageFromPath

• lang/java/ipc/converter.go: added recognition for src/test/java/, src/main/kotlin/, and src/test/kotlin/ path prefixes

zh(optional):

(Optional) Which issue(s) this PR fixes:

Fixes #95 #146

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