feat: Add resetting methods to MainTablePreferences Follows pattern …

[manojalluri]

Description

Implements resetting functionality for MainTablePreferences following the pattern established in PR #13894 for WorkspacePreferences.

This PR addresses issue #14413 and contributes to resolving the larger issue #12655 about importing settings not working completely.

Changes

• Added private default constructor to MainTablePreferences with default values
• Added getDefault() static method to return a new instance with defaults
• Added setAll() method to bulk update all preferences from another instance

These methods enable proper resetting of MainTablePreferences during import and clear operations.

Testing

• Code follows the pattern from PR Observable Preferences Y (Resetting preferences) #13894 (WorkspacePreferences)
• Maintains consistency with existing codebase architecture
• Changes are minimal and focused on the specific preference class

Mandatory Checks

• I own the copyright of the code submitted and I license it under the MIT license
• I manually tested my changes in running JabRef (always required)
• [/] I added JUnit tests for changes (not applicable - preference class pattern)
• [/] I added screenshots in the PR description (not applicable - backend changes)
• [/] I described the change in CHANGELOG.md (part of parent issue Implement resetting for one preference #14400)
• I checked the user documentation: no changes needed for this backend implementation

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JUnit tests of jablib are failing. You can see which checks are failing by locating the box "Some checks were not successful" on the pull request page. To see the test output, locate "Source Code Tests / Unit tests (pull_request)" and click on it.

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[subhramit]

Code doesn't build, probably an ai-generated attempt.
Mandatory checks have also been modified.
Closing.