refactor(merge,split,json): adopt streaming approach and standardize types, address gradle warnings

[balazs-szucs]

Description of Changes

This pull request introduces several improvements and refactorings focused on memory efficiency, stream-based file handling, and code simplification, especially for handling large files such as ZIP archives and CBZ-to-PDF conversion. The most significant changes include switching from byte-array-based file processing to streaming via InputStream, optimizing CBZ-to-PDF conversion to reduce memory usage, and generalizing field access patterns for better code clarity.

File streaming and memory efficiency:

• Added retrieveInputStream and storeInputStream methods to FileStorage, enabling streaming file reads and writes instead of buffering entire files in memory. This is crucial for handling large files efficiently.
• Refactored TaskManager.extractZipToIndividualFiles to use streaming extraction from ZIP files, storing each extracted file directly via storeInputStream, and determining file size after storage. This eliminates the need to buffer entire files in memory.

CBZ-to-PDF conversion improvements:

• Refactored CbzUtils.convertCbzToPdf to return a TempFile instead of a byte array, process images one at a time (reducing peak memory usage), and write the output PDF directly to disk. Also, Ghostscript optimization now writes to a new temp file if requested.

General code simplification and consistency:

• Replaced getter method calls with direct field access in several classes (such as OAuth provider, analytics settings, and role enumeration) for clarity and consistency.

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Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have read the How to add new languages to Stirling-PDF (if applicable)
• I have performed a self-review of my own code
• My changes generate no new warnings

Documentation

• I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• I have read the section Add New Translation Tags (for new translation tags only)

Translations (if applicable)

• I ran scripts/counter_translation.py

UI Changes (if applicable)

• Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• I have tested my changes locally. Refer to the Testing Guide for more details.

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Pull request overview

This pull request implements significant architectural improvements focused on memory efficiency and code modernization for handling large PDF files and archives. The changes include adopting streaming I/O patterns, standardizing data types from boxed collections to primitive arrays, and updating to Jackson 3 with Spring Boot 3 compatibility.

Changes:

• Introduced streaming file I/O via FileStorage.retrieveInputStream() and storeInputStream() methods, replacing byte-array-based operations for large files (ZIP, CBZ, PDF conversions)
• Standardized PDF JSON model types from List<Float> and List<Integer> to float[] and int[] for better memory efficiency and reduced object overhead
• Migrated to Jackson 3 (tools.jackson.databind.ObjectMapper) with backwards-compatible deserialization settings for primitives

Reviewed changes

Copilot reviewed 55 out of 57 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
frontend/src/core/hooks/tools/split/useSplitOperation.ts	Added empty string case handling in split endpoint selection
frontend/package-lock.json	Updated npm dependencies (iconify, posthog, svelte, autoprefixer, etc.)
build.gradle	Refactored syncAppVersion task with inline code; reduced LINE coverage threshold from 16% to 13%
app/core/src/main/resources/application.properties	Updated Spring Boot 3 error handling properties; disabled built-in ProblemDetails to use custom GlobalExceptionHandler
app/core/src/main/java/stirling/software/SPDF/model/json/*.java	Changed List to float[] and List to int[] across PDF JSON models
app/core/src/main/java/stirling/software/SPDF/service/PdfJsonConversionService.java	Updated to use primitive arrays; renamed isRealJobId to useLazyImages for clarity
app/core/src/main/java/stirling/software/SPDF/controller/api/converters/*.java	Updated return types from byte[] to StreamingResponseBody/TempFile for large file operations
app/core/src/main/java/stirling/software/SPDF/controller/api/SplitPdf*.java	Refactored split operations to use streaming ZIP output and TempFile instead of ByteArrayOutputStream
app/core/src/main/java/stirling/software/SPDF/controller/api/misc/ExtractImagesController.java	Changed to streaming ZIP creation, removed intermediate ByteArrayOutputStream
app/core/src/main/java/stirling/software/SPDF/controller/api/pipeline/PipelineController.java	Implemented streaming responses for single and multiple file outputs
app/core/src/main/java/stirling/software/SPDF/controller/api/pipeline/PipelineProcessor.java	Added MAX_UNZIP_DEPTH=10 limit to prevent zip bomb attacks; changed character literals
app/common/src/main/java/stirling/software/common/util/CbzUtils.java	Refactored to return TempFile and process images one at a time, reducing peak memory usage
app/common/src/main/java/stirling/software/common/util/PdfToCbzUtils.java	Changed to return TempFile with streaming ZIP creation
app/common/src/main/java/stirling/software/common/util/PdfUtils.java	Optimized single-image rendering by calculating dimensions mathematically instead of rendering
app/common/src/main/java/stirling/software/common/service/FileStorage.java	Added retrieveInputStream() and storeInputStream() methods for streaming file operations
app/common/src/main/java/stirling/software/common/service/TaskManager.java	Updated ZIP extraction to use streaming instead of buffering entire files in memory
app/common/src/main/java/stirling/software/common/model/ApplicationProperties.java	Changed getter calls to direct field access for OAuth and analytics settings
Multiple signature/form/provider files	Replaced String literals with character literals for single-character operations (e.g., '.' instead of ".")
Multiple controller/util files	Pre-compiled regex patterns as static constants for reuse

Files not reviewed (1)

• frontend/package-lock.json: Language not supported

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