This pull request adds a comprehensive set of new unit tests across several core modules, focusing on improving coverage for collections, conversion, file I/O, and JSON handling. The new tests verify immutability, edge cases, error handling, and correct fallback behaviors, as well as introduce a new test class for the StringToIterableConverter. These changes help ensure the robustness and reliability of the library's core utilities.

Collections:

• Added tests to verify immutability of ofList, ofSet, and ofMap methods in ListsTest, SetsTest, and MapsTest, ensuring that attempts to modify returned collections throw UnsupportedOperationException. [1] [2] [3]
• Added tests for additional behaviors in AbstractDequeTest, including removeFirstOccurrence, offer/poll sequences, and push/pop operations.

Conversion:

• Introduced a new test class StringToIterableConverterTest that covers acceptance, conversion, fallback, and priority logic for StringToIterableConverter and StringToCollectionConverter.
• Enhanced AbstractConverterTest with tests for hashCode, resolvePriority, and additional equality scenarios.

File I/O and Filtering:

• Added tests for StandardFileWatchService to cover starting, stopping, closing, and handling multiple listeners.
• Expanded FileExtensionFilterTest with cases for dot-prefixed extensions and filename filter acceptance.

JSON Handling:

• Added tests to JSONArrayTest and JSONObjectTest for invalid double values, fallback behaviors for optBoolean, optDouble, optInt, optLong, and optString, as well as write operations and exception handling. [1] [2]

Classloading:

• Improved AbstractURLClassPathHandleTest with a test for setting and restoring priority.