feat(helper-lines): allow lines override

[saif-ellafi]

PR Checklist (Required)

Please ensure your PR meets the following requirements:

• The commit message follows our guidelines: https://github.com/hm21/pro_image_editor/blob/stable/CONTRIBUTING.md#style-guides
• I have run dart format . in the terminal and committed any changes.
• I have run dart analyze . in the terminal and addressed any issues.
• I have run flutter test in the terminal and addressed any issues.
• I have pulled from the stable branch before committing.
• I have updated the CHANGELOG.md file with my changes (For the version, you can use X.X.X, I will later bump it after it's merged).
• The PR title follows the conventional commit style (e.g., feat(paint-editor): add new triangle shape).
• If this PR introduces breaking changes, I have verified that there is no way to implement the changes without them.

PR Type

Please indicate the types of changes this PR introduces by checking the relevant boxes:

• Bugfix
• Feature
• Performance
• Refactor (no functional or API changes)
• Code style updates (e.g., formatting, local variables)
• Documentation updates
• CI-related changes
• Other... Please describe:

Current Behavior

Since the Configs are immutable final, I would like a toggle button in my topbar to allow users to toggle helper lines on-demand (the zoom flag helps but it is not immediately noticed)

Issue Number: N/A

New Behavior

Allows an override helperLine config which is read in runtime without having to rebuild the editor allows to change the setting. We could remove final from the Configs or its attributes if preferred, but I assume it is not preferred, so I added as an override.

Breaking Changes?

Does this PR introduce a breaking change?

• Yes
• No

Additional Information

[hm21]

LGTM