Tiny CSL architectural cleanup

[subhramit]

Some quick architectural cleanups triggered by discussion at #12784 (comment).

• Free CSLCitationOOAdapter completely of preferences.
• Some related comments explaining usage of the initial style of generic style type to detect changes in styles in the adapter
• Only one instance of CSLUpdateBibliography needed - some more breathing space for the garbage collector.

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [/] Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• [/] Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• [/] Screenshots added in PR description (if change is visible to the user)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.