updated error handling and log levels for ShiftService

[EranTimothy-dev]

claimShift method updates

• Updated error handling in claim shift method to help with separate test cases and useful messages based on exception, for runtime exceptions and threading exception separately.
• usage of method level variable to store error message and format the message based on exception.

general changes

• Changed the log level from error to warn for logs that weren't an anomaly like row not being in the database.
• Removed commented out lines of code in LeaveServiceTest class.

[algotyrnt]

This pull request includes several changes to improve logging consistency, enhance error handling, and clean up unit test code. The most significant updates involve replacing logger.error with logger.warn for non-critical errors, refining exception messages for better clarity, and removing unused or commented-out code in tests.

Logging Improvements:

• Replaced logger.error with logger.warn for non-critical situations, such as when shifts or users are not found, across multiple methods in ShiftService. This ensures that the log level better reflects the severity of the issue. ([[1]](https://github.com/ShiftSL/backend/pull/86/files#diff-628a89f702a414d5e41cac2beac81aa3104f7f36f8da73bdec95a47832187c88L68-R76), [[2]](https://github.com/ShiftSL/backend/pull/86/files#diff-628a89f702a414d5e41cac2beac81aa3104f7f36f8da73bdec95a47832187c88L115-R128), [[3]](https://github.com/ShiftSL/backend/pull/86/files#diff-628a89f702a414d5e41cac2beac81aa3104f7f36f8da73bdec95a47832187c88L126-R139))

Error Handling Enhancements:

• Refined exception messages in claimShift to provide more detailed and user-friendly error descriptions. Added logic to include a lock-related error message when applicable. ([src/main/java/com/shiftsl/backend/Service/ShiftService.javaL95-R119](https://github.com/ShiftSL/backend/pull/86/files#diff-628a89f702a414d5e41cac2beac81aa3104f7f36f8da73bdec95a47832187c88L95-R119))

Unit Test Code Cleanup:

• Removed unused or commented-out ArgumentCaptor declarations in LeaveServiceTest to clean up the code and improve readability. ([[1]](https://github.com/ShiftSL/backend/pull/86/files#diff-99247d88923a0e0f2c05f38790ffa64d2ecda8546fc093aa96c1b7029d01a5ceL51), [[2]](https://github.com/ShiftSL/backend/pull/86/files#diff-99247d88923a0e0f2c05f38790ffa64d2ecda8546fc093aa96c1b7029d01a5ceL166), [[3]](https://github.com/ShiftSL/backend/pull/86/files#diff-99247d88923a0e0f2c05f38790ffa64d2ecda8546fc093aa96c1b7029d01a5ceL191))
• Simplified the requestLeaveTest by removing an unused variable assignment for the result of the method under test. ([src/test/java/com/shiftsl/backend/unittests/Service/LeaveServiceTest.javaL133-R132](https://github.com/ShiftSL/backend/pull/86/files#diff-99247d88923a0e0f2c05f38790ffa64d2ecda8546fc093aa96c1b7029d01a5ceL133-R132))